Skin under triple influences : gut, brain, skin microbiota
The skin has multiple functions: in addition to separating the body’s interior from the external environment1,2 it also protects against UV rays, plays a role in thermoregulation, gives us our sense of touch, and absorbs and synthesizes compounds.
Its barrier role is threefold. It acts as a physical barrier that protects the internal organs against environmental changes and pathogen invasions, a function aided by the continual regeneration of its epithelial cells.1,2,3The epidermis, dotted with hair follicles and glands that secrete lipids, antimicrobial peptides, enzymes, salts, and various other compounds, also acts as a chemical barrier: its acidic surface (pH between 4.5 and 5.5), which is often dehydrated, rich in salt, and with a relatively low temperature (29-34°C), make it a somewhat inhospitable environment for pathogens. Lastly, the keratinocytes in the epidermis act as an active immune barrier, monitoring for the presence of pathogens on the surface of the skin and, if necessary, triggering a host immune response.3,4,5
Despite this, the skin allows for the development of a commensal microbiota, or rather various skin microbiota whose composition varies according to the physico-chemical environment prevailing in a given skin area (face, armpits, etc.).
Like its counterpart in the gut, with which it communicates, the skin microbiota protects against pathogens, strengthens immunity and breaks down certain compounds.
Skin diseases associated with a dysbiosis
Modulating the skin microbiota
1 Ederveen THA, Smits JPH, Boekhorst J et al. Skin microbiota in health and disease: From sequencing to biology. J Dermatol. 2020 Oct;47(10):1110-1118.
2 Egert M, Simmering R, Riedel CU. The Association of the Skin Microbiota With Health, Immunity, and Disease. Clin Pharmacol Ther. 2017 Jul;102(1):62-69.
3 Barnard E, Li H. Shaping of cutaneous function by encounters with commensals. J Physiol. 2017 Jan 15;595(2):437-450.
4 Byrd AL, Belkaid Y, Segre JA. The human skin microbiome. Nat Rev Microbiol. 2018;16(3):143-155.
5 Bay L, Barnes CJ, Fritz BG et al. Universal Dermal Microbiome in Human Skin. mBio. 2020 Feb 11;11(1):e02945-19.
6 Chen YE, Fischbach MA, Belkaid Y. Skin microbiota-host interactions. Nature. 2018 Jan 24;553(7689):427-436.