Does your skin have a microbiome just as your gut has one? Scientists are discovering that the answer is yes. However in contrast to the gut microbiome, which is an excellent habitat for growth of fermentative bacteria, the skin is not as ideal. Most of the epidermal layer that protects us from the elements is salty, dry, acidic, and nutrient-poor. The areas around lipid-rich hair follicles are the exceptions.
Despite the inhospitable environment, a wide array and physiologically important categories of viruses, bacteria, archaea, and fungi are found on the skin. On average, the typical person has around 1,000 species of bacteria on their skin. And on average, the typical adult has approximately two square meters of skin, which provides unique ecosystems that create favorable conditions for various subsets of organisms.
The skin microbiome
The seeds of the skin microbiome begin at birth. The first microbes work to train the immune system to accept commensal organisms ,which have a neutral or beneficial impact on their host, while being alert to pathogens. These microbial communities grow and diversify until puberty. Then developmental and hormonal changes help determine the final composition that exists throughout adulthood.
Over the past decade, scientists have discovered evidence of extensive communication between skin cells, bacteria, and immune cells. This communication reinforces and repairs the barrier that the skin represents, lessens excess inflammation, and increases the body’s defenses against infection.
Disturbances in the skin ecosystem can leave the epidermal layer susceptible to immune hypersensitivity disorders like skin allergies or eczema. In addition, this may cause interference with regular healing of chronic wounds like diabetic ulcers.
Pinpointing the specific bacteria involved in these processes has proven to be difficult. Early studies labeled species such as Staphylococcus epidermidis and Staphylococcus aureus as the good and bad strains for dermatological health. But it’s becoming clear that each species might have several strains with distinct physiological activities. For instance, Cutibacterium acnes can produce metabolites that deter infection by pathogens, but certain strains of C. acnes seem to have a causative role in acne.
More functional and genetic studies are necessary to determine the factors that make a specific bacterium good or bad on the skin. Some studies seem very promising in making the determinations and producing innovative therapeutics. For example, some species, including S. epidermidis, produce compounds such as antimicrobials that might be used to treat infection.
The microbes may have therapeutic value as well. Clinical trials have indicated that transplanting a healthy gut microbiome can help to treat gastrointestinal conditions, such as inflammatory bowel disease. A similar approach could prove effective for dermatological disorders; administration of commensal skin bacteria can help to clear pathogenic species, such as S. aureus, that fuel inflammatory conditions, including atopic dermatitis.
For now, these diverse microbial communities remain poorly understood. But, unlike the gut, the skin is much more accessible. It may prove to be a promising pathway to understanding the biology of host–microbiome interactions.