Unit 1 Introduction to the Skin Disclaimer: Information offered on Herbal Academy web
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Unit 1 Introduction to the Skin
Disclaimer: Information offered on Herbal Academy websites is for educational purposes only. The Herbal Academy makes neither medical claim, nor intends to diagnose or treat medical conditions. Individuals who are pregnant or nursing, and persons with known medical conditions, should consult their licensed health care provider before taking any herbal product. Links to external sites are for informational purposes only. The Herbal Academy neither endorses them nor is in any way responsible for their content. Readers must do their own research concerning the safety and usage of any herbs or supplements. © Copyright Herbal Academy 24 South Road . Bedford, MA 01730 . 781-572-4454 Permission to make one copy for personal use is hereby granted to recipient.
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LESSON 1: GETTING STARTED WITH BOTANICAL SKIN CARE
WELCOME FROM DIRECTOR MARLENE ADELMANN
Visit the course to download the Botanical Skin Care Course welcome video transcript as a PDF.
WHAT YOU’LL LEARN
The Botanical Skin Care course is designed to give you a solid understanding of the structure and function of the skin and how skin care connects with whole-body wellness, and to show you how to make and use your own herbal skin and body care products. Your skin is your largest organ—on average, adults have about 21 square feet of skin! That’s a lot of cellular real estate to care for, and as you’ll learn in this course, the health of your skin is connected to the function of the rest of your body, as well. Fortunately, just like your skin, we’ve got you covered. In this course, we’ll use a holistic model of health in which we consider the wellbeing of the individual as a whole and explore the interconnection between diet, lifestyle, environment, and community with physical, emotional, and mental wellness. In the context of skin care, we’ll think about health on the inside and the outside, and we’ll specifically look at the importance of nutrition, lifestyle, digestive health, and liver function for maintaining healthy, vibrant skin throughout our lives. © Herbal Academy Botanical Skin Care Course: Unit 1
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Get ready for plenty of hands-on fun, too! We’ll guide you through all of the steps to create skin care products in your own kitchen, including which herbs and other ingredients to choose, and how to use them to create everything from herb-infused oils, herbal salves, and bath salts to hair care, facial toners, cosmetics, and skin creams. Finally, we’ll discuss specific herbs and preparations that can be used to support acute and chronic skin conditions, special considerations for aging skin, and how to create a complete skin care protocol for a range of skin types and concerns.
HERE’S HOW THE COURSE WORKS
Navigating the Course
Visit the course to download the Navigating the Student Dashboard video transcript as a PDF. Every unit contains multiple lessons that can be accessed by clicking on the Lesson tabs in the righthand sidebar. The subsequent unit will be accessible as soon as you pass the unit quiz, located at the bottom of the righthand sidebar (it will pop up once you read through each of the lessons in the unit). If you wish to return to the main course page from any lesson, simply return to your student dashboard to locate your courses.
Contacting Us
If you have specific comments or questions about the course material, logging in, course navigation, printing, and more, please first check the FAQ page (https://theherbalacademy.com/student-faq/). If you still need assistance, please contact us at [email protected]. © Herbal Academy Botanical Skin Care Course: Unit 1
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Multimedia
We have integrated graphics, videos, and recipes throughout the course to help illustrate the concepts discussed in the lessons. Graphics and video transcripts are downloadable as PDF files. We recommend you save these to your computer or print for future reference.
Recommended Reading and Resources
At the end of each lesson, you will find a list of recommended books and resources relevant to the lesson topics. We encourage you to consult any of the resources and references that are of interest to you to further your study of the topics and ideas presented in the course.
References
At the end of each lesson, you will find a list of references for the lesson content. Our lessons are thoroughly referenced to substantiate the concepts and information and to give credit where it’s due. As a general rule, any statement that is not common knowledge or that relies on other sources to develop is attributed to the author with a citation in the text and a reference in the bibliography. We encourage you to consult any of the references that are of interest to you to further your study of the topics and ideas presented in the course. Learning from multiple sources is a great way to cement your understanding of a subject, as there are many ways to explain even similar concepts.
Course Quiz for Completion Badge
At the end of Unit 4, there is a short set of feedback questions about the course and your experiences. Please answer these questions to receive your badge of completion. Your responses will support Herbal Academy in our quest to provide high quality, enjoyable, and affordable online herbal education.
MyHerbalStudies Facebook Community
A wonderful part of herbalism is community! Each individual has their own unique way of working with plants and we all learn from each other by sharing our experiences. Here at the Academy, our MyHerbalStudies Facebook Community is a place to engage in our school’s special herbal community. You can find the link to this group on your Student Dashboard or here (https://www.facebook.com/groups/ 1460100857651579/). Before you join this group, you must review our Group Guidelines (https://theherbalacademy.com/ wp-content/uploads/2018/11/MHS-GROUP-GUIDELINES-11_19_2018.pdf) and Tips for Receiving and Sharing Information (https://theherbalacademy.com/wp-content/uploads/2018/11/MHS-GROUP-DO- NOT-ASK-FOR-RECOMMENDATIONS.pdf). This is a thriving Facebook group exclusively for students at the Academy. The mission of this space is to provide a place to share tips, projects, and ideas, as well as news that might be of interest to the community. While there are many Facebook groups in which people discuss health advice and personal health challenges, it is our hope that the themes that will grow and blossom within this community space © Herbal Academy Botanical Skin Care Course: Unit 1
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focus on the lifelong herbal studies of our students and graduates, and their personal relationships to herbs and herbalism. As such, it is a unique space that will foster herbal creativity and celebrate the ways we all continue to learn. We look forward to getting to know each and every one of you and hope you will join us!
Everything is Printable (Except the Videos!)
Lessons, recipes, graphics, and video transcripts are printable! To print the course text for each unit, click the “Download PDF” button at the top of the course navigation menu on the far right. To print recipes, click on the small printer icon in the upper righthand corner of the recipe box. Note that all herbal recipe ingredients are in dried form, unless otherwise indicated. To print individual PDFs of graphics and video transcripts, click on the “Download PDF” button below that item in the lesson text. Please note: Internet browser behavior may vary. If your browser displays the date or other extraneous information when you go to print, try switching off headers and footers in your browser printing options.
Course Contributors and Teachers
If you haven’t already, please get to know us! You can learn about the Academy team and our fabulous contributing herbalist-writers here: https://theherbalacademy.com/about-us/.
We’re So Glad You’ve Joined Us Here – Now Let’s Get Started!
Disclaimer: The information presented in this course is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Check with your healthcare provider first if you have concerns about your health. In addition, you should speak with your healthcare provider or pharmacist before making adjustments to your diet or lifestyle and prior to introducing herbal and nutritional supplements as they may affect any treatment you may be receiving. You are advised to disclose any and all nutrient and herb supplements you are using to your healthcare team.
HISTORY OF HERBAL SKINCARE AND COSMETICS
In 2008, archaeologists in South Africa unearthed two abalone shells filled with an ochre, clay-based liquid preparation in a 100,000-year-old production workshop at Blombos Cave (Henshilwood et al., 2011). While it is difficult to surmise the exact purposes and means of application that this ground and liquified mixture of ochre, bone, and charcoal may have had, archaeologists conjecture that possibilities include decoration and skin protection. This finding suggests that humans have been interested in caring for, protecting, and beautifying the skin since prehistoric times. The continued quest for skin care practices and products that promise glow, vitality, and restored youth leads us to advanced (if not always appropriate) scientific formulations, ideally based on clinical evidence. As modern herbalists, learning from traditional plant-based methods of skin care can also inform, inspire, and guide us toward additional ways to cleanse, nourish, tone, and protect the skin in our beauty and self-care practices. Holistic practices of skin care and cosmetic adornment are as ancient as humankind’s longtime association of beauty with health and vitality. From an evolutionary viewpoint, this focus on skin care © Herbal Academy Botanical Skin Care Course: Unit 1
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and beauty makes sense: the condition and appearance of the skin conveys a lot of information about the state of wellness or imbalance in the body’s tissues and organ systems. In addition, applying substances such as clays, fats and oils, pigments, and resins to the skin has been a global practice since prehistoric times to provide physical and spiritual protection, detoxification, tissue healing, and beautification.
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Visit the course to download the Historical Timeline of Herbal Skin Care Worksheet as a PDF.
Health and Wealth: Skin Care and Social Status
The preparations and techniques used in skin care and decoration over the years also tell us about the societies that gave rise to them. In some places, certain oils, fragrances, and other substances were only obtained and used by the elite, with those of lower socioeconomic status using more basic and readily available items for self-care. In ancient Egypt, ordinary people were most likely to use castor, sesame, and moringa oil and simply prepared oils of spices and flowers in their preparations (Lucas & Harris, 2012). In contrast, the royal and wealthy were able to access specially prepared scented oils with resins, honey and dried fruits, and gemstones to powder and use as eyeshadow (Manniche, 1999). Depending on geography and historical context, a painted face could signify one’s readiness for war, social prominence as a landholder, or even one’s profession (for example, the Latin word lenocinium indicates both “makeup” and “prostitution”) (Hood, 2015).
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The Roots of Holistic Skin Care
Considering the long herbal traditions from Asia and the Indian subcontinent (herbal practice was discussed in the earliest Indian spiritual texts, dating back to 8000 BCE), we can imagine that many of the skin imbalances and concerns we have today are nothing new (Doniger, 2005). In ancient China, all kinds of skin care products—including facial masks, creams, steams, and oils—were commonly employed to cleanse, moisturize, rejuvenate, heal, and otherwise enhance the skin, but there was also a holistic focus to skin care. As we see today in traditional Chinese practice (and in holistic practices in general), an outer glow is a result of caring for the whole self, so the ancients also used nourishing foods, beverages, herbs, and fungi taken internally to support skin health (DeMello, 2012). Ancient ayurvedic practices, which originated among the earliest peoples of what is now India and Nepal, even included advanced rejuvenation systems such as kayakalpa, from the Sanskrit kaya (body) and kalpa (transformation), which encompasses diet, herbal teas, massage, and other therapies. Proponents of kayakalpa attribute to it the appearance of youth, changes to the hair and skin texture, and many other benefits (Patkar, 2008).
Plant Oils Were Central to Ancient Skin Care
Although times have changed, many ancient skin care preparations reflect materia medica and herbal actions that we can recognize and find useful today. For example, shea (Vitellaria paradoxa) nut, sesame © Herbal Academy Botanical Skin Care Course: Unit 1
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(Sesamum indicum) seed, and olive (Olea europaea) fruit oils have been used since ancient times to moisturize and protect the skin. While the term “antioxidant” was coined relatively recently, the concept of protecting tissue at the cellular level to maintain health (and a more youthful and vital appearance) has been around for ages. Archeological evidence points to a medieval shea butter production facility in the village of Saouga dating back to 1300 CE in what is now Burkina Faso, West Africa, from which shea butter was believed to have been shipped throughout Africa and the world (Neumann et al., 1998). Over a thousand years earlier, caravans were documented carrying clay jars of shea butter to the Egyptian kingdom during the time of Cleopatra’s rule. Cleopatra—not only a political ruler and strategist, but a beauty trendsetter—influenced the aesthetics and rituals of Egyptians of her time. At the same time, the growth of economic and cultural exchange under her rule meant that new body and skin care products were constantly being introduced and traded. The Egyptians used shea butter in cosmetics and it is still used to protect the skin and hair from the piercing, hot sun and dry winds of the savanna and desert (National Research Council of the National Academy of Sciences, 2006). The use of aromatic oils, unguents (ointments or healing salves), and other cosmetics (most famously, eye paints) in ancient Egypt has been confirmed by archaeological evidence dated as early as 4000 BCE (Mendoza, 2017; Tapsoba et al., 2010), and this trend quickly spread to the Mediterranean basin. Oils (necessary to protect and nourish the skin in hot, dry climatic conditions) were such an important staple in this geographic region that they were even included as part of workers’ wages (Ruiz, 2001)! In the 2nd century CE, the Greek physician Galen created cold cream (an emulsification of rosewater, almond or olive oil, and beeswax), which became the first commercially produced skin care product and a precursor to modern-day skin care creams (Sherrow, 2001). Oils were likewise revered in ancient India—the Sanskrit word for oil (sneha) translates to both “love” and “oil.” The benefits of applying various oils and fats to the body, such as sesame oil, ghee, and castor oil, is described at length in the Caraka Samhita, an ayurvedic text written approximately 2,500 years ago (Dash & Sharma, 2014). This tome, along with other texts written in the vedic period of India, includes many recipes for medicated oils, known as taila, some with 50 or more herbal ingredients (Mehta & Sharma, 2005)! Indigenous people in and around the Sonoran and Mojave deserts have historically used jojoba (Simmondsia chinensis) nuts and oil to support skin integrity and to address a variety of skin imbalances. This includes the Yavapai and Papago (native to what is now Arizona and Mexico) and the Cahuilla (of what is southern California), who have traditionally used jojoba in addressing wounds and sores, as a food and beverage, and for skin and hair conditioning (Native American Ethnobotany Database, n.d.; Niethammer, 1999). As in ancient Egypt, the use of nutritive oils to protect the skin and retain its moisture is an important part of maintaining healthy skin in such a hot and dry climate! Join clinical herbalist Ayo Ngozi Drayton as she recreates a historical recipe for Galen’s Cold Cream in the video below!
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Visit the course to download the Making Galen’s Cold Cream video transcript as a PDF.
Illusions of Vitality and Wealth: Early Cosmetics
For the earliest physicians, there was little distinction between medicine, skin care preparations, and cosmetics; perhaps this is because so many of the ingredients used to enhance beauty (such as oils and herbs) were also used to enhance wellness. Though their work was separated by 500 years, the Greek physician-philosophers Aristotle (c. 350 BCE) and Galen of Pergamon (c. 150 CE) both discussed beauty, aesthetics, and cosmetics in their writings, even to the degree of correlating these to energetics, humors, and physiological function. However, in their respective times, there was also growing debate and controversy surrounding the role of the physician in encouraging cosmetic practices. Many practitioners, including Galen, acknowledged a division between those substances and practices that enhanced beauty and those rooted in artifice or creating an illusion of robustness and beauty (Johnson, 2016). While Galen eschewed the latter, there was no stopping the ancient practices of augmenting one’s looks; in ancient Greece, Rome, and empires with which they traded, rosy cheeks, a sign of robustness and youth, were created with pigments from madder (Rubia tinctorum) root, mulberry (Morus spp.) fruit juice, or orchil, a dye obtained from red lichens (Kapparis, 2018). Here’s a modern take on an ancient cosmetic preparation you can try at home. You’ll find a detailed tutorial on how to make salves and balms in Unit 3, Lesson 2 of this course; if this is your first time making salve, you may want to watch the video in that lesson before trying this recipe.
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Alkanet Lip Balm Alkanet (Alkanna tinctoria) is thought to get its name from the Arabic al-hinna—literally, “the henna”—testament to its historical appearance and use. In Egypt, the Middle East, and India, alkanet was used as a red dye, in place of or in combination with henna (Lawsonia inermis) leaf. While the henna plant couldn’t be grown in Europe, alkanet could, and it became a popular dye as well as a cosmetic coloring agent (Miczak, 2001). Alkanet also has antimicrobial, demulcent, and vulnerary qualities, so it makes an excellent addition to a salve for the lips. This balm is moisturizing to the lips and a pretty red color, too! Adjust the amount of alkanet root powder based on the depth of color you would like to achieve. Ingredients 1-2 tsp alkanet (Alkanna tinctoria) root powder 1 tbsp (0.5 fl oz) coconut oil 1 tbsp (0.5 fl oz) olive oil 1½ tsp shea butter 1 tbsp beeswax ⅛ tsp vitamin E oil Up to 10 drops vanilla (Vanilla planifolia) CO2 extract or coriander (Coriandrum sativum) essential oil (optional)
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Directions ● Combine alkanet powder, coconut oil, olive oil, and shea butter in a double boiler over low heat (or a glass or ceramic bowl over a small saucepan of simmering water), stirring occasionally until completely melted. The red coloring of the root will begin to saturate the oil immediately. Use a cooking thermometer to monitor the temperature, keeping it below 120 degrees F. ● Once butter has melted, keep the oil mixture warm to allow alkanet’s pigments to saturate the oil. Simmer water in double boiler for approximately 30 minutes—keep an eye on the water level so that it doesn’t evaporate completely. ● Remove from heat and strain through several layers of fine cheesecloth or a natural coffee filter to separate the oil from the alkanet powder. ● Return strained oil to double boiler and add beeswax, warming until melted. ● Remove from heat and let cool a bit, then stir in vitamin E oil and essential oil (if using). ● Pour into tins or tubes and allow to cool. ● Once cool, label and date the tins. This preparation should keep for about 6 months in a cool, dry place (longer, if stored in the refrigerator).
Henna – Lawsonia inermis (Lythraceae) – Leaf
Henna is an example of an herb used traditionally as a cosmetic and dye, widely recognized for the distinctive reddish stain it imparts to hair, skin, and nails. It has been used throughout Africa, the Middle East, and the Indian subcontinent since antiquity for both therapeutic and cosmetic purposes. In the 14th century BCE, Queen Nefertiti of Egypt was known to stain her nails a blood-red color using henna, and it’s still used today in many parts of the world to decorate the hands and feet. Actions: Antibacterial, antifungal, antiparasitic, antipyretic, astringent, vulnerary Energetics: Cooling and drying Use: Henna leaf is combined with water to make a distinctive, lasting dye that ranges in color from bright red-orange to deep brown; the final shade of the dye when applied to skin, hair or cloth can vary depending on the dye preparation, site of application, and the amount of the molecule, lawsone, that’s present in the leaf (Cartwright-Jones, n.d.). Although leaf powder is most typically seen in commerce in North America, the seed, bark, and root of Lawsonia inermis are also used in African and Indian traditional medicine (Yadav, 2013). Henna leaf is traditionally used both internally and externally to cool inflammation, to address
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imbalances and diseases including measles, polio, and malaria, and for illness affecting the blood (Zumratdal & Ozaslan, 2012). Many pharmacologic and animal studies have explored various uses of henna, particularly its antimicrobial, anti-inflammatory, and wound-healing properties. In one trial, adding henna to a pharmaceutical gel preparation used to dress burn wounds led to enhanced skin healing through increased fibroblast attachment and proliferation, collagen secretion, and antibacterial action (Hadisi et al., 2018). In another study, henna paste showed significant antifungal activity against six different pathogenic fungi, including ringworm (Gozubuyuk et al., 2014). While there’s an abundance of ethnobotanical information about the many uses of henna, no clinical trials have been published, although one fascinating case report suggests that topical application of henna was helpful in alleviating hand-foot syndrome, a painful side effect of chemotherapy (Yucel & Guzin, 2008). Henna is most commonly used in Western herbalism as a topical antifungal. Herbalist jim mcdonald reports that he has used it successfully to address fungal infections including ringworm, athlete’s foot, and onychomycosis (toenail fungus). According to mcdonald, “The thing that makes henna so useful in such cases is that the same constituent that is responsible for the dark red dye (lawsone) also possesses antifungal & antimicrobial properties…This means that during the time that the stain is visible, there is a 24/7 action of the lawsone on the skin infection” (mcdonald, n.d., para. 4). Safety: Although topical use of pure henna is generally quite safe, it’s very important to watch out for the use of “black henna”—which are products that contain other ingredients and are often adulterated with paraphenylenediamine (PPD), a chemical that makes it appear darker and take effect more quickly. PPD can cause severe contact dermatitis, and in sensitive individuals can trigger a life-threatening allergic reaction (Treister-Goltzman et al., 2016). Use of henna is contraindicated for individuals with glucose-6-phosphate dehydrogenase deficiency (also known as favism), an inherited disorder (Gardner & McGuffin, 2013). And, of course, henna does stain the skin and fingernails! This typically lasts from 1-3 weeks, but varies depending on the type of henna and individual skin (mcdonald, n.d.). Dose: Recommended for topical use only.
THE ORIGINS OF SOAP
In many ancient cultures, the significance of skin care and cosmetic preparations extended beyond the care and healing of the physical body and were not as strictly delineated as the Greek physicians may have believed. From a philosophical perspective, both cleanliness and beauty were considered to be sacred principles. Ancient Egyptians worshipped deities that were representative of these principles and ritual cleaning and bathing was required of physicians, those in the priesthood, and those who attended to the beauty of others (such as manicurists, hairdressers, and perfumers) (Manniche, 1999).
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Although the earliest form of soap (consisting of water, oil, and an alkali such as lime or ashes) was documented in ancient Babylon in around 2800 BCE, ancient people used water, oils, and plant materials in various forms to stay clean (Toedt et al., 2005). Our ancestors around the world noticed that bathing with certain plants, such as soapwort (Saponaria officinalis), soap bark (Quillaja saponaria), agave (Agave spp.), yucca (Yucca spp.), and horsetail (Equisetum spp.)—which often grew conveniently near waterways—left them cleaner than bathing without them (Toedt et al., 2005). We now know that all these plants contain saponins, plant compounds that serve as natural surfactants, which are foaming detergents.
Ancient Skin Care Had Its Risks!
In Africa, the Middle East, and eventually Greece and Rome, people of all genders and social rank decorated their eyes with kohl (a lead-based mineral eye makeup usually comprised of the mineral galena, but often adulterated with soot). Kohl (along with crushed malachite and other gemstones) is what gave ancient Egyptian rulers their signature “cat eye” look, translated today as eyeliner and eyeshadow. Not only was kohl said to protect against the curse of the evil eye, a paste of kohl and fats was also antimicrobial, repelled flies and other insects, and could trap dust and other debris before it reached the eyes (DeMello, 2012). We know now that the same compounds used by the ancients to line their eyelids can be poisonous, depending on dose. Galena, a natural mineral containing lead, was the prevalent compound in kohl and only a very tiny amount of this naturally occurring substance is considered safe. Exposure to lead has been shown to impede the development of the brain and nervous system among the most vulnerable (babies, children, and pregnant individuals and fetuses), and is linked to learning disabilities and behavior difficulties, even with low-level chronic exposure (United States Food and Drug Administration, 2019). From ancient Egypt to 19th-century America, pale skin was a symbol of social status, evidence of having the wealth to avoid working outdoors. Unaware of the risks, people used white lead powder to give the appearance of lighter skin, while red lead, cinnabar, and other dangerous pigments were used to add a bloom to the cheek. Belladonna (Atropa belladonna)—whose potential toxicity earned it another common name, deadly nightshade—was used by Italian women of the Renaissance period to dilate the pupils, thus increasing their beauty—unfortunately, it could also lead to permanent blindness (Stewart, 2009)!
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Even in the last century, ingredients which we know today to be highly hazardous, such as mercury, were commonly included in skin and hair care preparations for years after their dangers became known (DeMello, 2012). Today, there are still harmful substances to avoid in products available on the market. Fortunately, there are many resources available to consumers (such as those created by the Environmental Working Group, online at www.ewg.org) that can help you make the cleanest and most nontoxic choices for your own care. An increasing number of companies have also begun to offer natural, nontoxic, and sustainably sourced skin and body care products and cosmetics. Of course, learning to formulate and develop your own herbal skincare regimen and preparations can be an even better way to ensure the quality and efficacy of your products. You’ll be well-equipped to do just that as you progress through the lessons and units of this course! Before you get started, we recommend taking a peek at your own skin and the organ systems that influence it in the worksheets we have provided below.
YOUR PERSONAL SKIN PROFILE
Energetics
Now that you’ve gotten a taste of the long history of herbal skin care, let’s take a look at how we can apply some classic principles from ancient healing traditions to modern skin care—starting with your own skin! You’re probably familiar with the standard skin “types”: oily, dry, and combination. These are based on easily observed qualities and tendencies of the skin, and they describe both how our skin tends to behave and a potential underlying imbalance. These are relative qualities—there’s no exact benchmark for what constitutes oily skin, and all oily skin is certainly not the same! These qualities can also change over time; we may have oily skin as a teen that becomes dry and sensitive as we age. As herbalists, we can use the basic energetic categories of Western herbalism—hot, cold, damp, and dry—to provide a more nuanced view of skin health. Using this energetic framework, we can identify the herbs, nutrition, and lifestyle practices that can help bring us back into balance. And unlike the standard skin “types,” these energetic principles don’t apply just to what’s happening on the surface of the skin: they can also give us insight about what’s happening inside the body. From a holistic health perspective, that’s crucial, since we know that what’s happening in our skin isn’t isolated from what’s happening in the rest of our body—or in our mind and spirit, for that matter! © Herbal Academy Botanical Skin Care Course: Unit 1
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To get started thinking about the skin in these terms, take a look at the descriptions in each category below. Which patterns do you see in yourself? Keep in mind that your skin characteristics are not likely to be in only one category—your skin may be hot and dry, hot and damp, cold and dry, or cold and damp. You may even have different energetic patterns on different parts of your body; a classic example is the oily “T” zone of the face, along the forehead, nose, and chin, combined with dry skin on the cheeks. You can also see this in acute skin conditions—if you touch some poison ivy (Toxicodendron radicans), you might end up with a hot, damp, weepy, and irritated rash on your hands, but the skin on your face will remain cool and dry. Remember, this presentation may change throughout your life, and even through the seasons of the year.
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Keep these concepts in mind as you progress through the lessons; we’ll return to them in more depth in Unit 3 and 4, where we’ll explore their application when formulating herbal skin care products.
Additional Observations
As herbalists, we know that the health of the skin is inseparable from the health of the rest of the body; as you’ll learn in this course, the function of the liver and the digestive system are particularly important for maintaining skin health. The digestive system and the liver work together to break down and eliminate much of what we take into our body—whether that’s through our diet or through our skin. If the liver and digestive system are not doing that job efficiently, we can build up pro-inflammatory compounds that contribute to a host of skin problems, ranging from acne and very dry skin to eczema and psoriasis. We’ll talk about how this all works, and what to do about it, later in the course. For now, here are a few points to help you begin to assess how these systems are working in your body.
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Visit the course to download the Symptoms of Internal Imbalance worksheet as a PDF.
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If you’re ticking many of these boxes and you have skin complaints, you may find you’ll benefit from taking an “inside-out” approach to skin health. You’ll learn more about that in Unit 2, where we’ll cover the connections between digestion, liver function, and skin health.
CONCLUSION
Exploring the history of herbal skin care gives us a sense of how much things have changed (and how much they’ve stayed the same!) through the centuries that humans have been using plant products to cleanse, beautify, tone, moisturize, and more. As modern herbalists, we can dig into our history and find so much to inform our skin care materia medica—from old favorites such as rose (Rosa spp.) petals and shea (Vitellaria paradoxa) butter to potentially new herbal allies such as alkanet (Alkanna tinctoria) root and madder (Rubia tinctorum) root. As you proceed through the Botanical Skin Care Course, we encourage you to carry this historical inspiration into your learning and remember that you’re following in some very ancient footsteps! With a little bit of history to inspire you and your personal skin profile in your toolbox, you’re ready to dive into learning about the nature of the skin, the factors that influence it, and the herbs and preparations that can bring balance to this important organ. Before you know it, you’ll be making your own skin care history!
RECOMMENDED RESOURCES
Beauty and Cosmetics 1550-1950 by Sarah Jane Downing Classic Beauty: The History of Makeup by Gabriela Hernandez Cosmetics and Perfumes in the Roman World by Susan Stewart Historical Recipes from Colonial Williamsburg: http://www.history.org/almanack/life/homebeauty/index.cfm Painted Faces: A Colourful History of Cosmetics by Susan Stewart
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LESSON 2: ANATOMY OF THE SKIN
INTRODUCTION
In this lesson, we’ll cover the basic structures that make up the skin. These structures are organized into two main layers, the epidermis and the dermis, which are both made up of multiple sublayers. While it’s not crucial to memorize all of the names of the various layers and the cells they contain, a basic understanding of the anatomy of the skin can give a lot of insight into how it functions and help us understand how to use herbal preparations effectively to support it.
Image: Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014,” https://en.wikiversity.org/wiki/WikiJournal_of_Medicine/Medical_gallery_of_Blausen_Medical_2014. WikiJournal of Medicine 1(2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work. Used under CC BY 3.0 license, https://creativecommons.org/licenses/by/3.0/legalcode.
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THE EPIDERMIS
As the outermost layer of our skin, the epidermis is the part of us that has the most contact with the outside world, and, as such, it has a primary protective role. The epidermis is considered specialized epithelial tissue; like the epithelial tissue that lines our mouth, digestive tract, and other mucous membranes, epidermal tissue regenerates very quickly and is continually replacing itself with new cells. When these tissues are injured, they can usually heal quickly. Unlike our mucous membranes, though, most of the cells of the epidermis produce and store keratin, a protein that gives skin, nails, and hair much of their strength and water resistance. The epidermis is avascular: it doesn’t contain capillaries, so all oxygen and nutrients needed by the cells of the epidermis are supplied by the blood vessels in the dermis. If you cut or scratch yourself and see blood, that means you’ve reached the dermal layer. In most places, the epidermis is only about 0.1 millimeters thick—about the thickness of a sheet of paper—so reaching the dermal layer isn’t very hard to do! For the most part, the epidermis is made up of four distinct layers, or strata; on the palms of the hands and soles of the feet, however, there’s an additional extra-tough water-resistant layer. Moving from the outside to the inside, these layers are called the stratum corneum, stratum lucidum (this is the additional layer that’s found only on the palms and soles), stratum granulosum, stratum spinosum, and stratum basale.
Image: Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014,” https://en.wikiversity.org/wiki/WikiJournal _of_Medicine/Medical_gallery_of_Blausen_ Medical_2014. WikiJournal of Medicine 1(2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work. Used under CC BY 3.0 license, https://creativecommons. org/licenses/by/3.0/legalcode.
All the layers of the epidermis except the lowest layer (the stratum basale) are comprised mostly of keratinocytes, the specialized cells that make and store keratin. The stratum basale contains mostly basal cells, which produce keratinocytes. Picture the epidermis as a sort of keratinocyte escalator: as the basal cells divide, producing new keratinocytes, older cells are pushed up toward the surface of the skin. Only the deepest cells receive oxygen and nutrients from the blood vessels in the dermis, so as they move upward, cells begin to die off and harden. By the time they reach the outermost layer (the stratum corneum), the cells are dead, dried out, and eventually just slough off. It takes about a month to shed and replace all of the cells of the stratum corneum (Biga et al., 2018). As keratinocytes move into the upper layers of the epidermis, they become anchored to each other through interlocking extracellular structures called desmosomes. Normally, as the cells of the stratum corneum age, these
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desmosomes break apart and we shed our skin as small particles (dust); however, desmosomes may remain intact in damaged skin, which is why sunburned or blistered skin can peel off in sheets (Biga et al., 2018). As our first point of contact with the outside world, the protective importance of the epidermis really can’t be overstated. In addition to acting as a physical barrier, it prevents passive water loss, protects against microbial infection, and prevents or reduces absorption of substances we come into contact with in the environment. Much of this protection occurs primarily in the stratum corneum and relies on what’s often called “barrier integrity.” Let’s take a deeper look at the stratum corneum to understand how this works.
Barrier Integrity: The Stratum Corneum
As a keratinocyte moves into the stratum corneum, its lipid (fatty) cellular membrane develops into a resistant cell wall that’s much less susceptible to water loss in a process called cornification. As these cells cornify, the lipids in the cell membrane are squeezed out into the intercellular space and the cells flatten, harden, and die. These specialized, hardened keratinocytes are called corneocytes. Together, corneocytes and the intercellular lipids form a “brick and mortar” structure, with the corneocytes acting as bricks and the lipids acting as mortar to hold them together (Wickett & Visscher, 2006). This lipid mortar is absolutely crucial for effective barrier integrity, including prevention of water loss. We’re not just talking about staying hydrated for glowy-looking skin here: mammals can’t survive if the skin doesn’t keep water (and electrolytes) circulating inside the body, rather than evaporating into the atmosphere! This is where ceramides come in. Ceramides are a particular type of lipid molecule that, along with cholesterol and free fatty acids, make up the bulk of the lipid portion of the stratum corneum. Synthesized ceramides, which are designed to act in the same way as the ceramides that are naturally produced within the keratinocytes of the epidermis, are now included as ingredients in some skin lotions and topical treatments. Natural ceramides are derived from the fatty acids that we consume in our diet, so the types of fat we eat can have a big impact on the composition of ceramides, the lipid matrix of the stratum corneum, and ultimately on the effective barrier function of the skin. We’ll learn more about the role of dietary fats and proteins in creating healthy skin structure in Unit 2, Skin Care from the Inside. In addition to the lipid matrix found between the corneocytes, a compound called natural moisturizing factor (NMF), produced within the cells of the stratum corneum, is a key component in healthy barrier function. NMF is produced within the corneocytes and helps keep the skin moisturized by attracting water from the surrounding environment and from the lower layers of the skin (Weber et al., 2012). NMF and the lipid components of the stratum corneum help keep the skin supple and hydrated and are important factors in maintaining barrier integrity and preventing water loss through the skin.
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Image: Open Stax College, Anatomy & Physiology, Connexions Website, http://cnx.org/content/col11496/1.6/. Jun 19, 2013. Used under CC BY 3.0 license, https://creativecommons.org/licenses/by/3.0/legalcode.
Other Specialized Cells of the Epidermis
The skin has a range of important functions in addition to acting as a protective barrier, including hormone production, immune response, and metabolic elimination. In addition to the keratinocytes, specialized cells found throughout the layers of the epidermis are required to accomplish all of these feats.
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Visit the course to download the Epidermis, Specialized Cells & Their Functions worksheet as a PDF.
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THE DERMIS
Directly below the epidermis, connected to the underside of the stratum basale, is the dermis. (The prefix epi means “on,” so epidermis means “on the dermis.”) Whereas the epidermis is a relatively thin, protective membrane, the dermis is a much thicker bed of connective tissue and is up to 40 times as thick as the epidermis. Much of the dermis is composed of a matrix of collagen and elastin fibers, which are the structural proteins that give skin its mobility, elasticity, and tensile strength. Collagen also binds water, helping to keep skin hydrated. In the outer layer of the dermis, called the papillary layer, collagen and elastin are organized in a loose mesh, and a network of capillaries (tiny blood vessels just one cell wide) provide oxygen and nutrients to the cells in the deepest level of the epidermis. In the deepest layer of the dermis, called the reticular layer, collagen and elastin fibers are much more densely packed together, and larger blood vessels are more numerous. The primary cells found in the dermis are fibroblasts, which secrete collagen and elastin, and immune response cells, including mast cells and macrophage cells. (Mast cells are involved in the inflammatory response to allergens, but they have many other immune functions as well; macrophages are white blood cells that ingest and destroy dead cells, cellular debris, and foreign particles, such as bacteria.) Image: Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014,” https://en.wikiversity.org/wiki/Wiki Journal_of_Medicine/Medical_gallery_of _Blausen_Medical_2014. WikiJournal of Medicine 1(2). DOI:10.15347/wjm/ 2014.010. ISSN 2002-4436. – Own work. Used under CC BY 3.0 license, https://creativecommons.org/licenses/ by/3.0/legalcode.
Whereas the epidermis is primarily a protective, enclosing membrane, the dermis contains a number of structures, including hair follicles, sebaceous glands, sweat glands, blood vessels, lymphatic vessels, and nerves. Some of these structures—the hair follicles, sebaceous glands, and sweat glands—are situated deep in the dermis, but extend through the epidermis and open to the surface of the skin. As you can see in the images above, each hair is seated in its own follicle, a hollow opening that surrounds the shaft of the hair. The oil that naturally lubricates the hair and skin, called sebum, is produced in sebaceous glands that open into these follicles. © Herbal Academy Botanical Skin Care Course: Unit 1
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Below the dermis is the subcutaneous layer, also known as the subcutis or the hypodermis. This layer contains mostly adipocytes, or fat storage cells, and collagen fibers; it is sometimes referred to as the third layer of the skin, but more precisely it’s an associated structure—hypo means below, so the hypodermis is really below the skin, not part of the skin. The main function of the hypodermis is fat storage and structural integrity, connecting the skin to the fascia that surrounds the muscles. In most of the body, the muscles below our skin and fascia attach directly to our skeleton; for the most part, we move because skeletal muscle moves our bones. Facial muscles are unique in that they attach to other muscles or to the skin, which makes facial skin highly responsive to even the smallest movement of the muscles below (BBC Science, 2014). That’s why we’re able to form our many facial expressions and dynamic wrinkles, which appear and disappear as we move the facial muscles.
PERMEABILITY OF THE SKIN
Now that you understand how the skin is put together, let’s look at what this means for herbal skin care. As we’ve discussed, the epidermis, and specifically the stratum corneum, is the primary site of the skin’s barrier function. That’s a very important consideration when we’re thinking about keeping things inside the skin—preventing water loss and maintaining skin hydration—but it’s also important when we’re thinking about getting things into the skin using topical or transdermal herbal preparations such as baths, creams, compresses, or liniments. If we want our herbs or skin care products to really get into the skin, they have to at least be absorbed into that outermost layer; if we want them to go even deeper and enter the rest of the body, they’ll have to get all the way through the epidermis. After that, molecules that make it into the dermal capillary bed are home free—they’ll enter systemic circulation and can travel throughout the body!
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Visit the course to download the Skin Permeability worksheet as a PDF. Herbal constituents (and other things) can get across the epidermal barrier in one of three ways: they can cross directly into the cells (intracellular transport), they can cross in between cells (intercellular transport), or they can sneakily bypass the epidermis all together, entering through the openings of hair follicles or sweat glands that route directly into the dermis (transappendageal transport or shunt route). Remember that the hardened outer membranes of the corneocytes are highly water resistant and are interspersed with water-resistant lipids. That means the epidermis as a whole is lipophilic, or fat-loving, © Herbal Academy Botanical Skin Care Course: Unit 1
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and fat-soluble substances will have a much higher rate of absorption than those that are water soluble. We’ll talk more about choosing ingredients, solubility, and absorption in Unit 3, Making Herbal Body Care Products. Fortunately, there are a number of things we can do to increase the skin’s permeability and make it easier for water-soluble molecules and water-based preparations to pass into and through the epidermis (Miller, 2015): ● Increasing contact area and duration of exposure are simple starting points—more skin contact for a longer period of time means there’s more opportunity for substances to move into the skin. ● Occlusion, or covering the area of skin that’s exposed to the substance, can increase absorption by preventing evaporation and increasing temperature. ● Location, location, location! Application sites that have a high concentration of hair follicles and sebaceous or sweat glands (like the scalp and face) will increase the opportunity for absorption through the shunt or bypass route, while sites with thinner epidermal layers (like the wrist and neck) provide less of a barrier for intercellular absorption.
THE SKIN MICROBIOME
In recent years, research has begun to show that what’s on our skin may be just as important as what’s in our skin. Just as the digestive tract is home to dense colonies of bacteria and other microorganisms that make up the gut microbiome, the surface of our skin has its own microbiome that hosts a range of bacteria, fungi, viruses, and even arthropods. A single square centimeter of the human skin can contain up to one billion microorganisms (Grice et al., 2008)! Skin health relies on a symbiotic relationship with the microorganisms on its surface; we’re now learning that just as disruptions in the balance of gut flora can cause digestive disturbances like constipation and diarrhea, changes in the skin microbiome appear to be associated with skin disorders (Dréno et al., 2016; Sanford & Gallo, 2013). The organisms of the skin microbiome are more diverse and more variable than the cultures of other epithelial surfaces, including the mouth, colon, and vagina (Sanford & Gallo, 2013). The skin microbiome includes both resident organisms—that is, those that live on the skin all the time—and transient populations, and changes depending on who and what we contact. The composition of the skin flora also varies widely across the body, since we have many types of skin terrain; microorganisms like the bacteria Propionibacterium acnes that feed off of our normal sebum are mostly found on the face and back, but rarely occur on our arms and legs (Kong & Segre, 2012). These organisms, when out of balance, contribute to the development of acne—which is why we most commonly see acne on the face, chest, and back, and rarely see it on the extremities.
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Image: PD
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The initial composition of skin flora is established at birth, either through inoculation during vaginal birth or postnatal skin contact, but it continues to shift throughout life. Some of the factors that influence its makeup are fixed variables, such as age, sex, and ethnicity, while others are dependent on lifestyle and circumstance, including ultraviolet (UV) light exposure, skin pH, nutrition, alcohol consumption, hygiene, and stress or anxiety (Dréno et al., 2016). The microorganisms normally found on healthy skin may be beneficial or commensal (neither benefitting nor causing harm to the human host), rather than pathogenic (causing disease or illness). However, even indigenous bacteria can become pathogenic when there is a state of dysbiosis (imbalanced flora); Staphylococcus aureus are normal resident bacteria, but when overpopulated or in the face of poor immune function, they can cause what’s commonly called a “staph infection” (Dréno et al., 2016). And beyond causing infection, shifts in the balance of skin flora are also associated with chronic skin disorders, including dandruff and seborrheic dermatitis, acne, atopic dermatitis (eczema), and psoriasis (Sanford & Gallo, 2013). However, it’s not always clear which comes first: are changes in skin flora driving the disease or is the disorder causing the change in flora? Many skin microorganisms exist as part of a balanced ecology, helping to check the growth of more pathogenic organisms or preventing the overgrowth of normal flora. For example, P. acnes bacteria liberate antibacterial compounds from the skin sebum, creating an inhospitable environment for the virulent strains of Staphylococcus that cause illness and infection (Dréno et al., 2016). It’s true that P. acnes can trigger acne as a result of inflammation or imbalance, but without P. acnes in its balancing role in the skin ecosystem, we may be more prone to developing bacterial infection. We might be tempted to think of this microbiome as a host of potential pathogens that need to be kept in check by our immune system: a few organisms might be good, but too many organisms is bad, and a healthy immune response should keep too many organisms from invading. But that’s not quite accurate—the relationship between our internal immune system and the skin microbiome is much more nuanced, with some indigenous flora actually helping to regulate immune function. As skin microorganisms interact with immune cells, they can influence host immune response not just by stimulating the immune cells to respond, but also by mediating or directing that response, working cooperatively with the immune cells to help maintain skin health, eliminating viral infection, and preventing excess inflammation (Dréno et al., 2016). We might even picture the microbiome/immune system interaction as more of a dance than a battle!
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AGING SKIN
The structure of the skin changes microscopically over time, and as we age, the changes become increasingly visible. These changes aren’t inherently pathological; they’re normal processes of the human body, not a sign of disease or ill health—although cosmetic manufacturers might like you to think otherwise! However, some of these changes can leave us more vulnerable to skin damage and infection. Changes in the skin as it ages are often grouped into either “intrinsic aging”—things that will happen regardless of external influences—and “extrinsic aging”—things that happen as a direct result of diet, environmental exposure, or other outside factors. As we age, the activity of our fibroblast cells naturally declines; this means we produce less collagen, the tissue of the dermis begins to thin, and we see fine lines and wrinkles appear. Subcutaneous fat in the face generally decreases, the fat pad that makes youthful cheeks plump may drift forward and down, and we may even lose bone mass in the face—all of this means that our face shape can change as we age; this loss of tissue can contribute to the development of wrinkles as well. The epidermis also begins to atrophy and there’s a decrease in the contact area between the epidermis and the dermis. You’ll remember that the epidermis is utterly reliant on the blood vessels of the dermis below for all of its nutrients and oxygen; as this contact area decreases, so does the food and oxygen supply for the cells of the epidermis. That means cells are regenerated more slowly and the skin becomes more fragile, more easily injured, and takes longer to heal when wounds do occur (Nigam & Knight, 2008). © Herbal Academy Botanical Skin Care Course: Unit 1
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The slowdown in production of epidermal cells also means that skin becomes more rough and dry (Nigam & Knight, 2008); the development of extremely dry skin creates a feedback cycle in which the dryness is both exacerbated by and contributes to a breakdown in barrier function (Wickett & Visscher, 2006). In turn, the failure of barrier integrity creates a predisposition for contact dermatitis and microbial infection. We also see a decrease in the number of melanocytes and Langerhans cells distributed throughout the epidermis. Remember that melanocytes produce the melanin that both colors our skin and protects from UV damage, so a decrease in melanocytes can lead to skin that is more pale and more sensitive to sunburns and other UV damage. At the same time, vitamin D production in the keratinocytes is inhibited, so while we may be less able to tolerate UV exposure, we’re likely to need more time in the sun to produce adequate vitamin D. While we certainly can’t stop the process of aging, there are many other factors that can increase the visible appearance of wrinkles, fine lines, and pigmentation changes. In particular, the development of darkened spots on the skin, sometimes called “age spots,” and the appearance of heavy or deep lines and wrinkles are significantly influenced by extrinsic factors, including UV light exposure, tobacco use and other major sources of oxidative damage, and essential fatty acid deficiency and other nutritional imbalances. Extrinsic factors can be addressed through herbal, dietary, and lifestyle support, and we’ll cover these in greater depth in Unit 2.
CONCLUSION
By learning about the anatomy and physiology of the skin, we’re setting the stage for a deeper understanding of how and why we can care for our skin using both natural, homemade skin care products and a healthy diet and lifestyle. If this introduction to skin physiology has whet your appetite and you want more—or if you’d like to review these ideas in a different format—you may want to take a look at some of the videos and resources below.
RECOMMENDED RESOURCES
Boundless Anatomy and Physiology: Integumentary System, by Lumen Learning: https://courses.lumenlearning.com/boundless-ap/chapter/the-skin/ Integumentary System Introduction, a video series by Khan Academy: https://www.khanacademy.org/science/health-and-medicine/human-anatomy-and-physiology#integume ntary-system-introduction The Skin Microbiome in Disease States, a presentation explaining clinical research on the skin microbiome in clear language: http://www.nationalacademies.org/hmd/Activities/PublicHealth/microbialthreats/2013-MAR-18/Day2/Se ssion-4/Video-23-Segre.aspx
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LESSON 3: FUNCTIONS OF THE SKIN
You gotta have skin All you really need is skin Skin’s the thing that if you got it outside, It helps keep your insides in ~Allan Sherman, “(Heart) Skin,” 1964
INTRODUCTION
Millions of years ago, living creatures emerging from the oceans onto Earth’s terrestrial surface began to evolve to survive in their new surroundings, developing a host of physiological adaptations to protect and preserve their body systems in a dry environment. Some of our skin’s functions and structure are a result of this adaptation to a life on land. Like most of the body’s tissues, the skin is overwhelmingly comprised of water. But the skin also serves a role of paramount importance: helping to maintain the moisture balance of the entire body. Protection from dehydration is only one of the skin’s functions, albeit a critical one. At the same time, the skin is a sensory organ that transmits information based on both internal and external cues; plays an integral part in immune system function, metabolism, and temperature maintenance; and stores, secretes, and eliminates substances in and from the body. This lesson explores the basic roles and functions of the skin as a foundation for discussing its wellness and care.
THE SKIN AS A PROTECTIVE BARRIER
The skin provides a protective barrier between what is distinctly you and what is not. In an example of form following function, a metaphor often used to describe the anatomy of the stratum corneum (the outermost layer of skin) is that of bricks and mortar, in this case comprised of dead skin cells (hardened keratinocytes, or corneocytes) layered in a lipid matrix. The layers of dead skin cells in the stratum corneum protect our internal environment in many of the same ways that bricks and mortar protect inhabitants of a home: shielding against harsh weather, changes in humidity and temperature, and invaders of the pathogenic variety. The stratum corneum limits colonization by pathogens through a variety of means, including maintaining water balance and pH, the balance of normal microflora, and secretion of antimicrobial substances (Elias, 2007). The fusion of cells in a lipid matrix forms a barrier that is fairly impervious to water and other molecules, but as you learned in Lesson 2, skin does allow for some degree of absorption of many substances through transdermal absorption, so it is considered a semi-permeable barrier. Permeability is a function of the activity of lipids and proteins in the skin; it allows the skin to act as a defensive barrier while still permitting the absorption of some compounds (Elias, 2007). This is why topical herbal applications, from salves and balms to foot baths and poultices, can affect the whole body, and are not just used for afflictions of the skin! © Herbal Academy Botanical Skin Care Course: Unit 1
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While the physical structure of the skin allows the sort of protection that a physical wall would provide a home, chemical means of protection are also employed by the skin. In this case, skin cells (and the skin’s bacterial microbiome) secrete substances that trigger skin-protective mechanisms. The acid mantle—a naturally secreted protective film—is what provides the skin with its mildly acidic pH. This is one important way the skin keeps harmful microorganisms in check before they spread and cause infection. Another way that the skin provides chemical protection is through sweat, which contains the antimicrobial peptide (AMP) precursor protein dermcidin. When secreted from sweat glands, it acidifies the skin and can impede the development of certain bacterial species (Gallo & Nakatsuji, 2011; Grice & Segre, 2011). Melanin is another chemical produced in the skin that has protective qualities. This pigment is the substance that gives our skin its color—lighter skin produces less melanin, while darker skin produces more. Melanin is secreted by just 1% of skin cells, called melanocytes. Melanin has been shown to protect against photodamage to DNA caused by ultraviolet A (UVA) and ultraviolet B (UVB) radiation, a side-effect of sunlight exposure—this is especially significant because DNA damage from ultraviolet (UV) radiation can be a precursor to a variety of skin cancers (Brenner & Hearing, 2008).
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Visit the course to download the Skin Physiology & Function worksheet as a PDF.
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WOUND HEALING
When the skin is broken—as with a cut, scrape, burn, or even acne—cells both in the localized area and throughout the body mobilize immediately to repair the wound and restore barrier integrity. This occurs through a highly complex series of overlapping processes involving specialized cells and chemical messengers that is sometimes called the “healing cascade” (Tortora & Derrickson, 2009). Depending on the nature and location of the wound, the body utilizes one of two mechanisms to heal: tissue regeneration and tissue repair. When a wound is located at the skin’s surface and is limited to the epidermis, it heals through tissue regeneration. In tissue regeneration, basal epithelial cells replicate themselves, migrating across the wound in order to close the breach. This is followed by a thickening of the epidermis, which quickly restores the integrity of the skin as well as its function. Surface wounds generally leave little scarring because of the presence of adipocytes (fat storage cells) in the newly developed skin. They allow for a more seamless merging of wound edges.
Image: Open Stax College, Anatomy & Physiology, Connexions Web site, http://cnx.org/content/col11496/1.6/. Jun 19, 2013, used under CC BY 3.0 license, https://creativecommons.org/licenses/by/3.0/legalcode.
A surface wound can heal in a number of ways. Primary closure occurs when a wound is minor and its edges remain in close proximity, and it can happen in a matter of hours. Tools or techniques such as adhesives, suturing, or staples may be employed to close the wound more quickly. Secondary closure occurs when a wound is gaping and its edges cannot be brought together; oftentimes this type of wound is caused by underlying disease processes, as in the case of friction ulcers. In this case, healing is encouraged by allowing the wound to remain open, with tissue contraction and re-epithelialization bringing about healing over a more extended period of time (Martin, 2013). Wounds to dermal tissue heal through the more complex process of tissue repair. Deep wounds can impact the skin cells as well as sweat glands, hair follicles, blood vessels, and other tissues in the dermis. Unlike in superficial wounds, deep wounds cause fibroblasts to differentiate into myofibroblasts, © Herbal Academy Botanical Skin Care Course: Unit 1
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which among other functions secrete extracellular matrix proteins that facilitate wound closure. While tissue repair restores the skin’s integrity, the process may not restore function. For example, the rebuilding of hair follicles or nerves in the affected area does not occur in the more fibrous tissue generated through tissue repair. This is why scar tissue looks so much different than normal skin, lacking pores, hair, and often having a shiny appearance (Darby et al., 2014; Martin, 2013).
INNATE IMMUNITY AND THE SKIN
Innate immunity is the nonspecific set of immune defenses with which we’re born. Certain cells in the body—notably concentrated in the skin, gut tissue, and blood—are pre-programmed to express certain mechanisms that are activated quickly in response to infection. Innate immune responses, therefore, appear within seconds to hours of exposure to specific antigens (foreign substances that trigger an immune response). The fact that skin participates in immune function isn’t entirely surprising, considering its protective role. Bacteria found on the surface of the skin play a role in innate immunity from the time we’re born; pro- and anti-inflammatory substances secreted from skin cells also play an important part in immune responses. Simply put, when the barrier of the skin is compromised, the innate immune system is activated. The skin’s microbiome is critically important in its immune function. Supporting a healthy microbiome not only supports the skin’s protective function, but can also make a difference in conditions like psoriasis and acne, which are associated with bacterial species commonly found on the skin. Helpful microorganisms found on healthy skin, such as Staphylococcus epidermidis, occupy gaps and niches in the skin, preventing the colonization or overgrowth of pathogenic microbes and protecting against infection by these more harmful microorganisms (Gallo & Nakatsuji, 2011). Inflammatory skin conditions, such as psoriasis and atopic dermatitis, can adversely affect the healthy development of the stratum corneum. In such cases, the skin’s barrier function is generally decreased (Madison, 2003), leaving the skin susceptible to infection. The types and amount of cytokines (substances secreted by cells of the immune system) found in psoriatic skin, for example, are quite different than in healthy skin. The presence of these substances not only signals an immune challenge, but some cytokines also contribute to the impaired cornification of the skin barrier through their influence on cell communication and gene expression (Hänel et al., 2013). The innate production of AMPs by keratinocytes, mast cells, neutrophils, and sebocytes in the skin is another critical way the skin protects against infection by pathogens; some AMPs also release cytokines that trigger proinflammatory responses. Interestingly, many of the protective AMPs on the skin are produced not by epidermal cells, but by microorganisms living on the skin’s surface, including Lactococcus, Streptococcus, and Streptomyces species (Bastos et al., 2009). C-type natriuretic peptides, hormones synthesized and secreted in the endothelium, are closely related to AMPs and modulate bacterial development in both balanced and imbalanced inflammatory states (Gannesen et al., 2018). In summary, there are many complex ways that the skin’s innate immune function protects us. Not only do several types of skin cells produce substances that keep pathogenic bacteria in check, our own native bacteria support immunity as well. The skin’s microbiome secretes some of the same antimicrobial substances as human cells, all to support the physical barrier of the skin.
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ADAPTIVE IMMUNITY AND THE SKIN
Image: Open Stax College, Anatomy & Physiology, Connexions Web site, http://cnx.org/content/ col11496/1.6/. Jun 19, 2013, used under CC BY 3.0 license, https://creativecommons.org/licenses/ by/3.0/legalcode.
Innate immune responses in the skin tend to be acute and short-lived, with peptides (protein components, which can act as signalling molecules), cytokines, and other endogenous substances springing into action quickly in response to invading pathogens. Adaptive immune responses, on the other hand, are specific, slower acting, longer lasting, and involve cell memory. Both of the major types of dermal antigen-presenting cells—Langerhans cells and other dermal antigen-presenting cells—initiate adaptive immune responses in the skin, but can differ greatly in their function and the immune mechanisms they stimulate and inhibit (Banchereau, 2008). Adaptive responses are also executed by the actions of both T-cells and B-cells, the major cells involved in adaptive immunity. T-cells in the epidermis can even be considered a “skin specific immune system” (Clark, 2010, p. 2), because of their range of functions: they perform cell surveillance within the epidermis, are capable of natural killer cell-like responses against immune threats, and can secrete cytokines that facilitate immune responses (Salmon et al., 1994).
Most B-cells migrate from lymphatic tissues to the skin as part of the adaptive immune response (although they sometimes occur in healthy skin tissue, where they may play a role in immunosurveillance and maintaining skin homeostasis). When the skin’s immunity is challenged—as in chronic inflammatory skin conditions, melanoma, and other imbalances—B-cells can take on a variety of roles to maintain the skin’s homeostasis. B-cells can initiate, maintain, or suppress inflammation; produce local and systemic antibodies; and may even play a role in the expression of T-cell-mediated imbalances, such as psoriasis (Egbuniwe et al., 2015). Much remains to be known about the roles and functions of B-cells in the skin. Both T- and B-cells are able to rearrange their DNA code in a way that allows their antigen receptors to recognize any antigen, but certain T-cells are responsible for documenting and storing immunologic memory for decades so that they are able to provide a rapid response in the case of a subsequent infection. Approximately 20 billion T-cells are present on the skin’s surface—nearly twice the number present in the body’s entire blood circulation—and these cells are capable of producing local immune responses (Clark, 2010). There are several types of T-cells present in the body, and each plays a slightly
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different role. T-cells found in the skin include regulatory T-cells, which protect against autoimmunity and assist in resolving skin inflammation, Th17 T-cells, which protect against pathogens, and effector memory T-cells, which protect against reinfection by pathogens in the long term. Like B-cells, T-cells have complex ways of encouraging or suppressing inflammation. Some skin microbes may play a role in priming T-cells to respond to similarly marked antigens (Gallo & Nakatsuji, 2011). Until relatively recently, it was believed that T-cells entered skin tissue only in cases of active inflammation. It was assumed that the high T-cell counts associated with inflammatory skin disorders like psoriasis were caused by migration of T-cells out of circulation and into the skin. However, researchers found that blocking T-cell migration made no difference in symptoms of psoriasis. As it turns out, T-cells within the skin contributed to the inflammatory condition through local action (Clark, 2010).
BODY TEMPERATURE MAINTENANCE
Our body’s systems and functions work constantly to support homeostasis, a crucial state of physiological stability and balance; certain factors, such as temperature and pH balance, must be tightly regulated in order for us to survive. Change in skin temperature is a primary factor that influences thermoregulation; humans (and other homeotherms) generate heat through their metabolic processes and release that same amount of heat into the environment to maintain temperature stability. While 98.6 degrees F (37 degrees C) is commonly thought of as standard, normal body temperatures actually fall within a wide range, reaching as high as 100 degrees F (37.8 degrees C), depending on many variables including age, sex, and time of day (Sund-Levander et al., 2002). When the body’s temperature is higher than normal, thermoreceptors in the skin sense and communicate the change to the hypothalamus, and the autonomic nervous system (ANS) initiates body-cooling mechanisms; blood vessels dilate, bringing more heat from the body’s core, which maintains a temperature of about 100 degrees F (37.8 degrees C), to the skin’s surface. Interestingly, the majority of the skin’s blood flow serves to maintain a stable body temperature; the amount of blood passing through skin tissues is between 20 and 30 times the amount necessary to nourish cells (Sherwood, 2012)! Image: Adapted from Open Stax College, Anatomy & Physiology, Connexions Web site, http://cnx.org/ content/col11496/1.6/. Jun 19, 2013, used under CC BY 3.0 license, https://creativecommons.org/ licenses/by/3.0/legalcode.
Sweating is another way the skin regulates temperature. Sweating is an evaporative heat loss mechanism controlled by the sympathetic branch of the autonomic nervous system. When sweat is released from the glands, © Herbal Academy Botanical Skin Care Course: Unit 1
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the temperature of the skin causes evaporation and the release of excess heat, thus cooling the body. Ambient humidity affects how effectively sweat cools the body, because water vapor saturation limits how much moisture can be taken up by the air. (This is why hot weather feels so much more extreme when it’s humid!)
When the body’s temperature is too low, the opposite actions occur in the circulatory system. Upon initial exposure to cold, thermoreceptors in the skin detect the drop in temperature and trigger an uptake in norepinephrine, causing the constriction of blood vessels in the skin and even in skeletal muscle. This provides an insulating effect, retaining heat at the body’s core. It’s also the same process that triggers goosebumps, which are caused by the contraction of the arrector pili, small muscles attached to hair follicles in the skin. (In animals with dense fur, this contraction causes the hairs to stand on end, creating a thicker insulating layer—but in most humans this doesn’t do much to keep us warm!) If the cold stress is not soon resolved, sympathetic nerves cause vasodilation to increase blood circulation to the surface, protecting the skin against damage such as frostbite. Cutaneous blood vessels then cycle between vasoconstriction and vasodilation, balancing the need to retain heat and supply blood to the skin. When cold stress is severe or prolonged, the body also generates heat through shivering, a reflex action of the skeletal muscles.
THE SKIN AS A SENSORY ORGAN
The skin is one of the primary interfaces between our internal body and our environment. Not only do the skin’s anatomical features and mechanisms make skin protective in physical and chemical ways, they also allow for sensory perception—thanks to the skin, along with the other sense organs, we can take in information about our environment. The cutaneous senses are the skin’s ability to perceive touch, temperature, pain, pressure, itch, stretching, hair movement, and even chemical stimuli. Our cutaneous senses allow us to experience not only pleasurable touch, but also sensations that are uncomfortable or painful, even serving as warning signals to keep us away from harm—for example, the sensation of extreme heat is a clear sign to back away from fire. Image: Adapted from Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014,“ https://en.wikiversity.org/wiki/Wiki Journal_of_Medicine/Medical_gallery_of_ Blausen_Medical_2014. WikiJournal of Medicine 1(2). DOI:10.15347/wjm/2014. 010. ISSN 2002-4436. Used under CC BY 3.0 license, https://creativecommons.org /licenses/by/3.0/legalcode.
Although most of the sensory organs (tongue, eyes, ears, nose) are found on the head, our sense of touch relies on tactile receptors that are spread all over the body’s surface, with concentrated areas on the skin of the face, hands, and genitals. Both sensory and sympathetic nerves of the autonomic nervous system (ANS) innervate the skin, branching off to the sweat glands, blood vessels, and © Herbal Academy Botanical Skin Care Course: Unit 1
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arrector pili. Nerve fibers in the skin terminate in tactile corpuscles that serve as receptors for sensory messages; this information is then transmitted to the sensory cortex of the brain.
VITAMIN D SYNTHESIS AND STORAGE
Vitamin D is an essential nutrient; it’s required for the body to function properly, but cannot be entirely synthesized by the body on its own. Precursors to vitamin D—technically, a prohormone and not a vitamin—are synthesized and stored in the skin. When the skin is exposed to sunlight, UV rays penetrate the skin and through a process called photolyzation, produce cholecalciferol. Cholecalciferol is converted in the liver to calcidiol before finally being converted by the kidneys into calcitriol, the active form of vitamin D. Most of our vitamin D intake comes from this process, but vitamin D can also be obtained from dietary sources, including dairy, fish, organ meats, and fungi that has been exposed to UV light, and through supplementation. Like hormones, vitamin D binds to receptors; these are present in nearly every cell in the body. Because of this, vitamin D has far-reaching effects on body functions and processes, from absorption of calcium in the bones to healthy nervous system, immune system, cardiovascular system, thyroid, and adrenal function. For this reason, vitamin D deficiency can affect a wide range of body systems and is implicated in a host of imbalances (Mostafa & Hegazy, 2015). The skin is both a production site and a target tissue for vitamin D. Some of the many functions of vitamin D include activity in cell proliferation, differentiation, and cell death (apoptosis), hair follicle cycling, wound healing and photoprotection, and antimicrobial activity on the skin’s surface. Because of the many interconnected ways that vitamin D interacts with the skin, deficiency is also implicated in a long list of dermatological imbalances, including skin cancer, psoriasis, ichthyosis, atopic dermatitis, hair loss, acne, and autoimmune skin conditions such as systemic lupus erythematosus (SLE) (Mostafa & Hegazy, 2015). Although it is unclear whether vitamin D deficiency is causative or a consequential effect of inflammation, it is clearly linked to poor health (Autier et al., 2014). A number of factors can influence vitamin D levels; nutrient deficiency, skin color and type, the use of sunblock, environment/location, time of year, clothing choices, and behavior (such as avoiding the outdoors on sunny days or using a sun umbrella) all have an impact. Depending on where you live, you may receive more or less vitamin D through sunlight exposure—while sunlight exposure in many tropical regions is more than adequate to synthesize sufficient vitamin D, residents above far northern and southern latitudes do not synthesize sufficient vitamin D between the months of October and March (Webb et al., 1988). (Some research suggests this may apply to anyone living above 37 degrees N or below 37 degrees S of the equator (Holick, 2006)—which includes about half the United States and most of Europe!) Melanin, the pigment that gives skin its color, absorbs and scatters UV radiation that reaches the epidermis; as a result, the conversion of vitamin D precursors to vitamin D is slower and less efficient in darker-skinned people than in those with lighter skin (Bonilla et al., 2014).
WATER, LIPIDS, AND THE SKIN
Sweating is not the only way that water passes through the semipermeable epidermal barrier. Water is also lost through a diffusive and evaporative process called transepidermal water loss (TEWL). Healthy skin loses between 100 and 150 milliliters (mL) of fluid per day through this process, driven by the diffusion of moisture from the body into the much drier external environment; skin (and in particular, the stratum corneum) adapts dynamically to moisture changes in the environment by increasing or decreasing its permeability as needed (Sparr et al., 2013). © Herbal Academy Botanical Skin Care Course: Unit 1
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Environmental inputs such as temperature, air circulation, humidity, light sources, and radiation can affect the process and increase water loss in a manner that can affect the skin’s physical properties and appearance, as well as its enzymatic and chemical mechanisms. High rates of TEWL, for example, can slow cell regeneration and wound healing and influence pH levels; conversely, as skin heals, rates of TEWL are lowered (Gorcea et al., 2013). Intrinsic factors such as the location and type of skin, skin color, and ethnicity also affect the rate of water loss from the skin (Rogiers et al., 2005; Singh et al., 2000). Permeability and water loss are also affected by lipids (fats or oils) produced in the skin. There are many types of lipids that make up the skin’s lipid layer, including free fatty acids, cholesterol, phospholipids, glycolipids, and ceramides. Many of these lipids form a complex mixture called sebum, a protective layer that helps to waterproof the skin and acts as a barrier against pathogens and debris. (Note that not all of the oils on the skin’s surface are sebum—some lipids on the skin are secreted from skin cells, and others come from sweat and environmental matter.)
Image: CNX OpenStax, https://cnx.org/contents/[email protected], used under CC BY 4.0 license, https://creativecommons.org/licenses/by/4.0/legalcode.
Sebum is secreted from sebaceous glands located all over the skin (with a few exceptions, including the palms of the hands and the soles of the feet). These glands develop as part of the epidermal tissue during embryogenesis, beginning as clumps of undifferentiated cells that form outgrowths from hair follicles before fully differentiating into sebocytes. For this reason, most—though not all—sebaceous glands are connected to hair follicles, where the two along with the arrector pili muscles make up what is called the pilosebaceous unit. Many functions are attributed to sebum, including photoprotection, antimicrobial activity, and immune activity. Sebocytes are biologically active epithelial cells, expressing receptors for peptides, neurotransmitters, and steroid and thyroid hormones, but much remains unknown about how exactly sebum is produced, its metabolic pathways, and even its ultimate role in human health (Michniak & Wertz, 2005; Picardo et al., 2009; Zouboulis, 2009). However, recent findings have indicated that © Herbal Academy Botanical Skin Care Course: Unit 1
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adiponectin, a protein hormone that is involved with breaking down fats and maintaining glucose levels, seems to play an important role in sebocyte function (Jung et al., 2017).
CUTANEOUS ABSORPTION AND METABOLISM
While the stratum corneum acts as a waterproofing barricade, it also must be permeable enough to allow keratinocytes to remain hydrated and to prevent fissures or other tissue damage that could compromise the skin’s integrity. Lipids play an important role in cutaneous absorption. The “mortar” of the skin’s brick-and-mortar-like structure is composed of lipids that differentiate into impermeable crystalline regions surrounded by more fluid regions that facilitate the uptake of water (Forslind, 1994). As we discussed in Lesson 2, many other substances can be absorbed by the skin, through the follicles, glands, and the epidermis itself. How they are absorbed and metabolized depends on the type of substance, its solubility, and its molecular size. Once absorbed, most substances pass through all of the layers of the epidermis and dermis before being absorbed into the bloodstream or lymphatic circulation (Baynes & Hodgson, 2009). Some of the substances absorbed into the skin are also metabolized locally. While the liver is considered to be the main hub of metabolic processes in the body, other organs, including the skin, share the responsibility of transforming substances in the body. The skin commonly comes in contact with pharmaceutical drugs, ingredients from cosmetics and personal care products, and xenobiotics (synthetic compounds that can mimic endogenous substances in the body) in a number of ways, including topical and transdermal application and environmental exposure. These substances all need to be metabolized before they can be utilized by or excreted from the body; part of that metabolic process—phase I metabolism—typically occurs in the liver, but the second stage—phase II metabolism—can occur in the skin. We’ll cover metabolic processing in greater depth later in Unit 2, Lesson 1 of this course, when we discuss the eliminative functions of the skin.
CONCLUSION
As we have seen, the skin has a range of important functions. As a physical barrier, healthy skin is able to block the entry of pathogens and debris while keeping tissues underneath warm enough, cool enough, and hydrated enough for optimal function. As a chemical protector, it prevents damage from the sun’s UV rays, provides antimicrobial support, and responds to immune challenges. Our skin constantly communicates information about our environment, helps us to experience pleasure and pain, and even plays a role in nourishing us by generating vitamin D! Many inherent factors affect our skin’s function, including ethnicity and skin color, sex, skin type, body-mass index (BMI), and anatomic site. Other environmental factors, from extreme weather to illness, can also affect skin function, as can diet and lifestyle. Ultimately, the skin’s properties affect its function. In the following units, we’ll learn more about supporting both the structure and function of the skin with nutrition, herbs, and routine skin care.
RECOMMENDED RESOURCES
Anatomy and Physiology of the Skin by Paul A. Kolarsick, Maria A. Kolarsick, and Carolyn Goodwin: https://journals.lww.com/jdnaonline/fulltext/2011/07000/Anatomy_and_Physiology_of_the_Skin.3.aspx Functions of the Integumentary System, from Human Anatomy and Physiology: https://opentextbc.ca/anatomyandphysiology/chapter/functions-of-the-integumentary-system/ © Herbal Academy Botanical Skin Care Course: Unit 1
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Introduction to Skin Anatomy and Physiology and The Skin: Anatomy, Physiology, and Microbiology videos by Armando Hasudungan: https://armandoh.org/subjects/dermatology/
CONGRATULATIONS!
You have reached the end of Unit 1 in the Botanical Skin Care Course! This course is comprised of four units. To move on to the next unit, please take the quiz. You can find the “Take A Quiz” button at the bottom of your navigation bar on the right side of the screen. If you do not see the “Take A Quiz” button, click through the lessons in the navigation bar to make the button pop up! Happy studies!
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REFERENCES LESSON 1
Cartwright-Jones, C. (n.d.). Henna for Hair. Retrieved from http://www.hennaforhair.com/faq/index.html Cavallo, P., Proto, M.C., Patruno, C., Del Sorbo, A., & Bifulco, M. (2008). The first cosmetic treatise of history. A female point of view. International Journal of Cosmetic Science, 30(2), 79-86. https://doi.org/10.1111/j.1468-2494.2007.00414.x Dash, B., & Sharma, R.K. (2014). Caraka Samhita Vol. I. Varanasi, India: Chowkhamba Sanskrit Series Office. DeMello, M. (2012). Faces around the world: A cultural encyclopedia of the human face. Santa Barbara, CA: ABC-CLIO. Doniger, W. (2005). The rig veda. London, UK: Penguin Classics. Dyer, D., Dalzell, F., & Olegario, R. (2004). Rising tide: Lessons from 165 years of brand building at Procter & Gamble. Brighton, MA: Harvard Business School Press. Gardner, Z., & McGuffin, M. (Eds.). (2013). American Herbal Products Association’s botanical safety handbook. Boca Raton, FL: CRC Press. Gozubuyuk, G.S., Aktas, E., & Yigit, N. (2014). An ancient plant—Lawsonia inermis (henna): Determination of in vitro antifungal activity against dermatophytes species. Journal De Mycologie Medicale, 24(4), 313–318. https://doi.org/10.1016/j.mycmed.2014.07.002 Hadisi, Z., Nourmohammad, J., & Nassiri, S.M. (2018). The antibacterial and anti-inflammatory investigation of Lawsonia inermis-gelatin-starch nano-fibrous dressing in burn wound. International Journal of Biological Macromolecules, 107(Part B), 2008-2019. https://doi.org/10.1016/j.ijbiomac.2017.10.061 Hartmann, A. (2016). Back to the roots: Dermatology in ancient Egyptian medicine. Journal of the German Society of Dermatology: JDDG, 14(4), 389-396. http://doi.org/10.1111/ddg.12947 Henshilwood, C.S., d’Errico, F., van Niekerk, K.L., Coquinot, Y., Jacobs, Z., Lauritzen, S.E., … Garcia-Moreno, R. (2011). A 100,000-year-old ochre-processing workshop at Blombos Cave, South Africa. Science, 334(6053), 219-222. http://doi.org/10.1126/science.1211535 Hood, J. (2015). How to win a Roman chariot race: Lives, legends and treasures from the ancient world. London, UK: Icon Books. Johnson, M. (2016). Ovid on cosmetics: Medicamina Faciei Femineae and related texts. L ondon, UK: Bloomsbury Publishing. Kak, S. (n.d.). The Mahabharata and the Sindhu-Sarasvati tradition. Retrieved from http://www.ece.lsu.edu/kak/MahabharataII.pdf Kapparis, K. (2018). Prostitution in the ancient Greek world. Berlin, Germany: de Gruyter. Kleiner, D.E.E. (2005). Cleopatra and Rome. Cambridge, MA: The Belknap Press of Harvard University Press. Lowry, B. (2011). Her dream of dreams: The rise and triumph of Madam C.J. Walker. New York, NY: Vintage Books. Lucas, A., & Harris, J.R. (2012). Ancient Egyptian materials and industries. Minneola, NY: Dover Publications, Inc. Manniche, L. (1999). Sacred luxuries: Fragrance, aromatherapy, and cosmetics in ancient Egypt. Ithaca, NY: Cornell University Press. Mansell, K. (2004). Recreating a 2,000-year-old cosmetic. Nature News. Retrieved from https://www.nature.com/news/2004/041101/full/news041101-8.html mcdonald, j. (n.d.). Henna: Not just another pretty face. Retrieved from https://traditionalroots.org/henna/ Mehta, A.K., & Sharma, R. (2005). Ayurvedic pharmacy. Delhi, India: Chaukhamba Sanskrit Pratishthan.
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Mendoza, B. (2017). Artifacts from ancient Egypt. Santa Barbara, CA: Greenwood Press. Miczak, M.A. (2001). Henna’s secret history: The history, mystery and folklore of henna. S an Jose, CA: Writers Club Press. National Research Council of the National Academy of Sciences. (2006). Lost crops of Africa: Volume II: Vegetables. Washington, DC: The National Academies Press. Native American Ethnobotany Database. (n.d.). Jojoba. Retrieved from http://naeb.brit.org/uses/38056/ Neumann, K., Kahlheber, S., & Uebel, D. (1998). Remains of woody plants from Saouga, a medieval West African village. Vegetation History and Archaeobotany, 7(2), 57-77. http://doi.org/10.1007/BF01373925 Niethammer, C. (1999). American Indian Cooking: Recipes from the Southwest. Lincoln, NE: University of Nebraska Press. O’Brien, R.D. (2009). Fats and oils: Formulating and processing for applications (3rd ed.). New York, NY: CRC Press. Patkar, K.B. (2008). Herbal cosmetics in ancient India. Indian Journal of Plastic Surgery, 41 (Suppl.), S134-S137. Paye, M., Barel, A.O., & Maibach, H.I. (2006). Handbook of cosmetic science and technology. New York, NY: Taylor & Francis. Poucher, W.A. (1974). Perfumes, cosmetics and soaps: Volume II: The production, manufacture and application of perfumes. New York, NY: John Wiley & Sons, Inc. Ruiz, A. (2001). The spirit of ancient Egypt. New York, NY: Algora Publishing. Sherrow, V. (2001). For appearance’ sake: The historical encyclopedia of good looks, beauty, and grooming. Westport, CT: Oryx Press. Stewart, A. (2009). Wicked plants: The weed that killed Lincoln’s mother and other botanical atrocities. Chapel Hill, NC: Algonquin Books of Chapel Hill. Tapsoba, I., Arbault, S., Walter, P., & Amatore, C. (2010). Finding out Egyptian gods’ secret using analytical chemistry: Biomedical properties of Egyptian black makeup revealed by amperometry at single cells. Analytical Chemistry, 82(2), 457-460. https://doi.org/10.1021/ac902348g Thomas, E. (2016). Max Factor and Hollywood: A glamorous history. Charleston, SC: History Press. Toedt, J., Koza, D., & Van Cleef-Toedt, K. (2005). Chemical composition of everyday products. Westport, CT: Greenwood Press. Treister-Goltzman, Y., Egbaria, E., & Peleg, R. (2016). An allergic reaction to henna used in a traditional painting ceremony. The American Journal of Tropical Medicine and Hygiene, 94(5), 941-941. https://dx.doi.org/10.4269/ajtmh.15-0833 United States Food and Drug Administration. (2019). Lead in food, foodwares, and dietary supplements. Retrieved from https://www.fda.gov/food/foodborneillnesscontaminants/metals/ucm2006791.htm Yadav, S., Kumar, A., Dora, J., & Kumar, A. (2013). Essential perspectives of Lawsonia inermis. International Journal of Pharmacy and Chemical Sciences, 2, 888-896. Yucel, I., & Guzin, G. (2008). Topical henna for capecitabine induced hand–foot syndrome. Investigational New Drugs, 26(2), 189-192. https://doi.org/10.1007/s10637-007-9082-3 Zumratdal, E., & Ozaslan, M. (2012). A miracle plant for the herbal pharmacy; Henna (Lawsonia inermis). International Journal of Pharmacology, 8(6), 483-489. http://doi.org/10.3923/ijp.2012.483.489
LESSON 2
BBC Science. (2014). Human body and mind: Facial muscles. Retrieved from https://www.bbc.co.uk/science/humanbody/body/factfiles/facial/frontalis.shtml
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Biga, L.M., Dawson, S., Harwell, A., Hopkins, R., Kaufmann, J., LeMaster, M., … Runyeon, J. (2018). Integumentary system: Layers of the skin. In L.M. Biga, S. Dawson, A. Harwell, R. Hopkins, J. Kaufmann, M. LeMaster, … J. Runyeon (Eds.), Anatomy & physiology. Corvallis, OR: Open Oregon State, Oregon State University. Retrieved from http://library.open.oregonstate.edu/aandp/chapter/5-1-layers-of-the-skin/ Dréno, B., Araviiskaia, E., Berardesca, E., Gontijo, G., Sanchez Viera, M., Xiang, L.F., … Bieber, T. (2016). Microbiome in healthy skin, update for dermatologists. Journal of the European Academy of Dermatology and Venereology, 30(12), 2038-2047. http://doi.org/10.1111/jdv.13965 Grice, E.A., Kong, H.H., Renaud, G., Young, A.C., Bouffard, G.G., Blakesley, R.W., … Segre, J. (2008). A diversity profile of the human skin microbiota. Genome Research, 18(7), 1043–1050. https://dx.doi.org/10.1101%2Fgr.075549.107 Kong, H.H., & Segre, J.A. (2012). Skin microbiome: Looking back to move forward. Journal of Investigative Dermatology, 132(3), 933-939. http://doi.org/10.1038/jid.2011.417 Miller, T. (2015). Dermal absorption of essential oils. Naturopathic Doctor News & Review. Retrieved from https://ndnr.com/mindbody/dermal-absorption-of-essential-oils/ Nigam, Y., & Knight, J. (2008). Exploring the anatomy and physiology of ageing. Part 11–The skin. Nursing Times, 104(49), 24-25. Sanford, J.A., & Gallo, R.L. (2013). Functions of the skin microbiota in health and disease. Seminars in Immunology, 25(5), 370-377. http://doi.org/10.1016/j.smim.2013.09.005 Weber, T.M., Kausch, M., Rippke, F., Schoelermann, A.M., & Filbry, A.W. (2012). Treatment of xerosis with a topical formulation containing glyceryl glucoside, natural moisturizing factors, and ceramide. The Journal of Clinical and Aesthetic Dermatology, 5(8), 29. Wickett, R.R., & Visscher, M.O. (2006). Structure and function of the epidermal barrier. American Journal of Infection Control, 34(10), S98-S110. https://doi.org/10.1016/j.ajic.2006.05.295
LESSON 3
Autier, P., Boniol, M., Pizot, C., & Mullie, P. (2014). Vitamin D status and ill health: A systematic review. The Lancet Diabetes and Endocrinology, 2(1), 76-89. https://doi.org/10.1016/S2213-8587(13)70165-7 Banchereau, J. (2008). The long arm of the immune system. Scientific American, 18(3), 56-63. https://doi.org/10.1038/scientificamerican0708-56sp Bastos, M.C., Ceotto, H., Coelho, M.L., & Nascimento, J.S. (2009). Staphylococcal antimicrobial peptides: Relevant properties and potential biotechnological applications. Current Pharmaceutical Biotechnology, 10( 1), 38-61. Baynes, R.E., & Hodgson, E. (2009). Absorption and distribution of toxicants. In E. Hodgson, Ed. A textbook of modern toxicology.Hoboken, NJ: John Wiley & Sons, Inc. Bonilla, C., Ness, A.R., Wills, A.K., Lawlor, D.A., Lewis, S.J., & Smith, G.D. (2014). Skin pigmentation, sun exposure and vitamin D levels in children of the Avon Longitudinal Study of Parents and Children. BMC Public Health, 14(1), 597-607. http://doi.org/10.1186/1471-2458-14-597 Brenner, M., & Hearing, V.J. (2008). The protective role of melanin against UV damage in human skin. Photochemistry and Photobiology, 84(3), 539-549. https://doi.org/10.1111/j.1751-1097.2007.00226.x Clark, R.A. (2010). Skin-resident T cells: The ups and downs of on site immunity. The Journal of Investigative Dermatology, 130(2), 362-370. http://doi.org/10.1038/jid.2009.247 Darby, I.A., Laverdet, B., Bonté, F., & Desmoulière, A. (2014). Fibroblasts and myofibroblasts in wound healing. Clinical, Cosmetic and Investigational Dermatology, 7, 301-311. https://doi.org/10.2147/CCID.S50046 Egbuniwe, I.U., Karagiannis, S.N., Nestle, F.O., & Lacy, K.E. (2015). Tissue-resident immune cells: Revisiting the role of B cells in skin immune surveillance. Trends in Immunology, 36(2), 102-111. http://dx.doi.org/10.1016/j.it.2014.12.006
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