Just two decades ago we knew very little about the role of the microbiome in human health. Today, it’s one of the hottest topics in both the scientific literature and the popular media. But while most studies so far have focused on the microbes that live in the gut, researchers are now turning their attention to the skin microbiome—with fascinating results.
Skin is the largest organ of the human body. Healthy, intact skin helps our bodies to retain moisture and provides a protective barrier from physical stress and strain as well as from environmental pathogens.
Skin is composed of the outer epidermis and the inner dermis. Sweat glands and hair follicles with their associated sebaceous glands originate in the dermis and connect to the skin surface through the epidermis. The sebaceous glands form sebum, an odorless oily substance that keeps the skin and hair moist, effectively “waterproofing” it. The amount of sebum produced and retained in the skin varies depending on hormone levels and hygiene habits (1, 2, 3). Sebum also sets up what is known as the “acid mantle,” a protective barrier that places limits on the types of beneficial microbes and pathogens that are permitted to reside in the skin (4).
What role does your skin ecosystem play in your skin and overall health? And how can you actively cultivate a healthy skin microbial community?
Your Skin as an Ecosystem
Human skin hosts a diverse ecosystem of bacteria, fungi, viruses, mites, and archaea (5, 6). It is estimated that our skin harbors approximately 1 billion microbes per square centimeter (7). Just like any other ecosystem on earth, resident skin ecosystems vary depending on their location on the body and are controlled by moisture and temperature conditions; one’s gender, age, and genetics (8); and individual environmental factors (9, 3).
This skin ecosystem is established at birth, and its development is heavily influenced by the method of delivery. A baby born via the birth canal will be inoculated with Lactobacillus species from mom’s vaginal flora. A baby born via C-section will come into contact with mom’s skin ecosystem first and be seeded with that particular set of microbes (6). From there, the skin microbial community is cultivated by those who care for the infant and altered by routine hygiene practices, personal care products (10), types of clothing that touch the skin (11, 12), exposure to medications (7, 13), time spent in contact with others (14), and time spent in nature (5).
Skin Ecosystem and Disease
Researchers at the forefront of the skin microbiome field are just now beginning to understand how they can shed light on the relationship between microbial communities and disease. This study has been limited by methods of culturing microbes in widely varied “skin climates,” by techniques of genetic analysis, by the challenge of isolating microbes from skin material, and by the fact that current analyses measure the entire historical record of microbes (both living and dead), not just the microbes that may influence health at the present (15, 16, 7).
Nonetheless, new research suggests that there are changes in the skin microbial communities associated with many health conditions, including:
- Acne (17)
- Psoriasis (18)
- Atopic dermatitis, eczema (19)
- Tinea versicolor (20)
- Seborrheic dermatitis (dandruff, cradle cap) (21)
- Rosacea (22, 23)
- Vitiligo (24)
- Warts (25)
- Blepharitis (26)
- Malaria and attractiveness to mosquitoes (27)
What do these associations mean? Does this mean that if you suffer from rosacea you can find relief by changing the microbial community of your skin? This is one avenue of skin microbiome research, but researchers are finding that it’s not easy to draw clear conclusions.
Six changes you can make to encourage a healthy skin ecosystem
What we do know is that individual members of the skin ecosystem can suddenly change from commensal or beneficial to pathogenic (25, 28, 29, 30, 31). The best example of this is Staphylococcus epidermidis, the cause of staph infections. S. epidermidis is a common and innocuous member of the human skin ecosystem, except of course when it’s not innocuous. S. epidermidis produces different biofilms, has antibiotic resistance, and contains mobile DNA elements when recovered from hospital settings compared to natural human environments. The chimeric nature of some bacteria suggests that their presence or absence is not the primary cause of disease but that there is some environmental trigger controlling pathogenesis (30).
Rosacea has long been treated with antibiotics, suggesting a bacterial root for this common skin condition despite the fact that the mechanism by which bacteria might cause rosacea has not been established. Attempts to better understand the pathogenesis of rosacea have led researchers to investigate the role of the skin mite Demodex (an arachnid) (22). Demodex species inhabit the sebaceous glands of most people, existing on epidermal cells and sebum. People who suffer from rosacea have a higher density of Demodex in their skin, and while this correlation is interesting, it does not explain why rosacea responds to antibiotics. Jarmuda et al. (2012) propose that the bacteria Bacillus oleronius, which have been isolated from Demodex mites from rosacea patients, may be responsible for the rosacea condition.
Why then are some people more prone to higher density of mites? The answer may lie in the composition of skin surface that supports the community. One study demonstrates that the fatty acid composition of skin is significantly different between people with and without rosacea (23). Rosacea patients have reduced levels of long-chain saturated fatty acids, potentially compromising the integrity of the skin barrier. This insight opens the door to rosacea therapies that shift the fatty acid profile of the sebum.
There is a bigger picture unfolding with respect to skin microbial communities and disease, one where the microbes are opportunistic rather than necessarily pathogenic. A recent study suggests that people with immune deficiencies simply have more permissive skin (32) and that skin disorders are associated with compromised immunity. This study evaluated the skin microbiota of people with rare primary immunodeficiencies (PID) and atopic dermatitis compared to a healthy group. They discovered that the group with PID hosted microbes that were not seen in the healthy controls, including Clostridia species and Serratia marcescens (a common household microbe). The PID group also had less variation between skin ecosystems of the body. In other words, the skin ecosystems of people with decreased immunity are weakened, permitting colonization of opportunistic pathogens.
What Can You Do to Cultivate a Healthy Skin Ecosystem?
While skin microbiome research is in the “wild west” stage today, there are many things that you can do to be proactive about your skin health.
Redefine for Yourself What It Means to Be Clean
Soaps, fragrances, and personal care products may alter your skin’s ecosystem in a way that nature hasn’t intended. Wild animals take “dust baths” that effectively bathe their skin in soil bacteria that help to keep them clean. Products that contain preservatives and synthetic ingredients may change the pH of your skin and disrupt your natural ecosystem, particularly if you have decreased immunity.
Consider What Touches Your Skin
While you can’t see it, cosmetics have been found to alter the microbial composition of skin (34). Make-up has also been found to cultivate its own ecosystem with time (35). Get rid of old make-up and consider reducing the role that cosmetics play in your life.
Consider Your Clothes
Interestingly, researchers have investigated the microbial growth in synthetic vs. natural clothing. They have found that synthetic materials harbor bacteria that are not native to or are out of balance with the human skin ecosystem, while the microbial communities found in natural fibers mirror the skin microbial communities. Even more, it has been found that washing machines serve to disperse microbial communities among members of a household (12). Most dryers are not hot enough to kill microbes and may even promote growth if clothes are left damp. Air drying clothes in the sun may better disinfect clothing.
Consider Your Environment
Chronic exposure to sterile or otherwise unnatural indoor environments and the microbes that they support may permit opportunistic species to colonize your skin, particularly if you are already immune compromised. Exposure to natural microbial environments may promote a healthy human microbiome, inside and out (36).
Consider Your Overall Health
While the skin ecosystem is fascinating to study, it does not exist in a vacuum. Addressing only topical and environmental changes to support skin ecology is short-sighted, especially considering the influence of overall immune function on skin permissiveness. Check out my Nutrition for Healthy Skin e-book to better understand the nutrient requirements for optimal skin health, and my Gut Health e-book to learn how to support your immune system.
Reestablish Your Skin Microbiome
Although the research in this area is not yet robust, some evidence suggests that applying ammonia-oxidizing bacteria (AOB) can help to reestablish a healthy skin microbiome. These bacteria have populated our skin microbiome naturally, acting as peacekeepers for the microbial community, but widespread use of soaps, deodorants, and other personal care products wiped them out. Mother Dirt has a line of skin biome-friendly products (such as soaps, shampoos, and sprays) that contain AOB and can be used daily to improve skin health. I and many others in the Paleo community have used these products and found that they can either partially or completely replace conventional soaps and shampoos, with no increase in body odor.