Focus

Skin under triple influences : gut, brain, skin microbiota

The skin has multiple functions: in addition to separating the body’s interior from the external environment^1,2 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.