The gut microbiome has gotten much well-deserved attention, likewise with the emerging focus on the oral microbiome. By comparison, research and clinical attention towards the skin microbiome has been scant, although there isn’t a skin condition that I am aware of that doesn’t have some degree of “skin dysbiosis” associated with it, and arguably, we’ve assaulted our skin barrier and microbial ecosystem with soaps, sanitizers, deodorants and medications as significantly as we have our GI barrier and ecosystem.
Tolerance to the Skin Microbiome: New Research
I was absolutely struck by a November, 2015 paper from the journal Immunity, titled “A Wave of Regulatory T Cells into Neonatal Skin Mediates Tolerance to Commensal Microbes”. Researchers demonstrated in an animal model that there is a very brief flurry of massive T regulatory cell activity specific for establishing tolerance to the skin commensal microflora very early in neonatal development. When Treg cells were blocked entry to skin, tolerance towards commensals was inhibited. The authors also demonstrated that attempting to establish tolerance to the skin’s commensal microflora in adults was not possible, suggesting that this neonatal immune/microflora conversation is indeed critical.
Further, the authors showed that the flurry of Treg activity during this time was unique to the skin, and the skin commensal- sensitized Treg cells were found in circulation, suggesting global, not merely local, implications. The authors go onto hypothesize that interruption of this process likely has profound health implications in terms of chronic inflammation, allergic disease, autoimmunity. Co-author Michael Rosenblum, a dermatologist and immunologist at UCSF was quoted in The Scientist as saying:
“One major clinical implication of this study is giving antibiotics to a child in early neonatal life is likely a disservice because this will limit the amount and type of bacteria that is seen by the adaptive immune system and this could be linked to the development of autoimmune, inflammatory skin diseases later in life,”
While these findings need to be demonstrated in humans, it is not a far leap to think that early damage to the skin microbiome and the establishment of tolerance could have far reaching implications in us as well.
The Skin Microbiome: A Primer
Of the one trillion organisms residing on our skin, there are over 1,000 different bacterial species, up to 80 different fungi species, plenty of viruses and a few mites. The SALT- or skin-associated lymphoid tissue, is highly active. In fact, each square centimeter of skin contains over a million commensal bacteria and over a million lymphocytes. A one-to-one bug:lymphocyte ratio. Wow.
While the skin microbiome–like the gut microbiome– is relatively stable over time (despite environmental changes) the skin microbiome does vary depending on the “eco-niche,” or location. For instance, colonies change depending on the amount of light, the pH and whether the area is moist, warm, dry, hairy or oily. And the microbiome differs with age and gender: a hormonal, sweaty teenage boy sports a very different microbiome than a sedentary, post-menopausal woman.
The skin microbiome resides deep into the dermis and dermal adipose.
Once upon a time, we thought that our microbiome only existed on the surface of the skin and that the deeper dermal layers were sterile. We now know that’s not true. In 2013, scientists did a deep dive into the dermis looking for microbes. And they were identified– a diverse and somewhat distinct group– all the way down to the subcutaneous adipose, directly positioned to communicate with the host. While it couldn’t be determined with the DNA techniques used whether the organisms were viable, the bacterial components identified, including DNA, ATP and polysaccharide A, are all known to exert effects on host cells. Although much inter-individual variability exists, the dominant phylum identified was Proteobactera. More research is needed, but it’s likely here that the most intimate communication between the skin microbiome and our immune system takes place, and has been proposed by Zeeuwen, et al, the microbiome of the deeper layers may be regarded as the “host indigenous microbiome”.
Gut and Skin Microbiome: Shared, but Different
There are shared phyla on the skin and in the gut, (Firmicutes and Bacteroides are found in abundance at both locations), shared species include Staphylococcus, Streptococcus and possibly Candida, although the jury is out as to whether Candida is limited to skin infections only. Some hints of bifidobacterium have been noted the deeper stratum corneum and lactobacillus species are more commonly found in females.
The major microbiome players of the skin:
Sebaceous areas: Propionibacteriaceae, Staphylococcaceae, Corynebacteriaceae
Moist areas: Staphylococcaceae, Corynebacteriaceae Actinobacteria (phylum)
Dry areas: Proteobacteria (phylum), Staphylococcaceae, Corynebacteriaceae, Bacteroidetes (phylum)
Malassezia species appear likely to be the dominant fungal organism identified on healthy skin.
A robust skin microbiome protects against infection or dysbiosis in much the same way a good gut microbiome does, by colonization resistance (i.e. crowding out overgrowth of pathogenic organisms) and by maintaining relatively acidic environment (pH is around 5.0), which inhibits growth of pathogens. Staphylococcus epidermidis, a major commensal bacterium, produces phenol-soluble modulins that inhibit pathogens such as S. aureus and Group A Streptococcus. Commensals can also inhibit inflammation through cross-talk via
Toll-like receptors 2 and 3, and stimulate production of antimicrobial peptides such as cathelicidin, which can kill bacteria, fungi and viruses.
The microbiome aids in wound healing, limits exposure to allergens and UV radiation, minimizes oxidative damage and helps to keep the skin barrier intact and well-hydrated.
Tending the Skin Microbiome
We’re very familiar with the idea that excess cleanliness, antibiotics and other medications damage the gut microbiome and increase the risk of allergy and autoimmunity, among other issues.
Ditto for the skin microbiome. Excess use of antimicrobial hand sanitizers, cosmetics and soaps are all potential factors contributing to skin dysbiosis, barrier damage and antibiotic resistance. An imbalanced microbiome, or skin dysbiosis, is associated with many skin conditions, including psoriasis, allergies, eczema, contact dermatitis, acne, poor wound healing, skin ulcers, dandruff, yeast and fungal infections, rosacea and accelerated skin aging.
We’ve undoubtedly significantly altered our skin microbiome with our “clean addiction.” Take soap, for example. By its very nature, it’s alkalinizing. But recall that our skin microbiome prefers a pH of about 5. At this relatively acidic pH, the healthy microbiome thrives. It’s also understood that the opportunistic bacteria — the dysbiotic players — do better at a higher, more alkaline pH. And soap has a pH of about 10! Thus, we’re altering our microflora and skin barrier with soap, setting the stage for imbalance.
Interestingly, recent study showed that kids who hand-wash dishes have a lower incidence of allergies compared to those in families that use a dishwasher. That sounds paradoxical given what I’ve just mentioned about soap, but the authors speculate that this has to do with the benefits of skin exposure to the microbes on the dirty plates.
Topical steroids are well-understood barrier destroyers and internal medications (such as antibiotics, oral steroids, acid blockers, and non-steroidal pain relievers) also likely damage the skin microbiome.
Finally, I haven’t come across research in the area of toxins and the skin microbiome yet, but it seems safe to assume that common toxins found in skin products such as parabens, phthalates, sulfites are not useful to the microbiome.
Recently, I published a piece on the skin microbiome for www.mindbodygreen.com. I included some basic ideas for tending to the skin microbiome that I’ve include here:
1. Eat healthy and stay hydrated.
I recommend good fats (Omega 3’s and monounsaturated fatty acids) proteins, carbohydrates, colorful vegetables and clean water. Keep processed foods and extra sugar out of the diet. Research shows that what you put in your mouth indeed influences your skin and skin microbiome in many ways. Keep food organic as much as possible.
3. Take care of your gut.
Arguably, many skin issues are influenced by the gut microbiome, and gut health in general. I recommend taking a daily high-quality probiotic. Research exists on the use of probiotics in preventing or treating many skin conditions.
4. Minimize the use of hand sanitizers and soaps.
Let your microbiome thrive! If you find that reducing your showers and soaps leads to you becoming too oily or odoriferous, I recommend consulting with a functional medicine doctor to find out why. And there are many non-toxic, natural moisturizers and cleansers you can try instead.
5. Work up a sweat a few times a week.
If you’re eating well, I suspect that the sweat you produce is likely fortifying for the skin microbiome. Research on “skin prebiotics” will surely prove interesting.
6. Keep your stress levels in check.
Just like elsewhere in the body, stress likely negatively influences what’s happening with your skin. Find a stress management method that works best for you, such as yoga or meditation.
7. Try a topical probiotic.
This is a new, growing area. In my practice, I recommend patients try applying a probiotic powder mixed with coconut oil or shea butter to their skin. Emerging research on using kefir or yogurt on skin looks promising as well.