Skin constitutes the major organ of the body, with a main role of protection from the external environment, representing a composite ecosystem since it harbours a number of microbial communities including bacteria, fungi and viruses living in distinct niches. The role of the skin microbiota is of paramount importance since it is involved in multiple host functions such as defence against pathogens, toxin degradation and host immune system maturation.
It seems essential, for a good functionality of such features and to maintain skin homeostasis, that communities inhabiting the skin remain in equilibrium. Indeed, it is well known that a number of skin inflammatory diseases are associated with shifts in the resident microbiota from a “healthy” to an “altered” state. For example, when a stress occurs, either endogenous or exogenous, the skin ecosystem loses its equilibrium, creating conditions that directly influence the balance of skin microbiota in terms of microorganisms number and their taxonomical composition.
This change represents a signal for skin immunity, which reacts activating an inflammatory response. If unbalanced conditions remain for a long time and the dysbiosis persists, chronical inflammatory episodes can occur. This condition can be associated with many skin pathologies such as dandruff, acne, psoriasis and atopic dermatitis.