The skin is the largest organ and the outermost interface between the human body and its environment. For decades, the skin surface was estimated to have an area as high as 2 m², but recently, by taking into account the appendages, the estimate has increased to as high as 25 m² [1]. Many regional differences overlap in the skin topography. For instance, temperature and humidity are higher at vaulted sites, such as the groin or armpit (approaching 37°C, the body’s core temperature) and lower at the body’s extremities (fingers and toes, approximately 30°C). Sebaceous gland density is an important variable factor involved in the secretion of many lipidic compounds, including fatty acids, that contribute to the acidification of the skin pH, which varies between 4.2 and 7.9 depending on the site of measurement [2].

These characteristics induce many possibilities for creating different ecological niches housing numerous commensal bacteria as well as fungi, viruses, archaea, and mites [3] in a network that varies in terms of its density and composition. Altogether, these microorganisms define the skin microbiota. According to Grice et al. [4], skin microbiota diversity may be higher than gut microbiota diversity. The vulnerability of this microbe network lies in the many intrinsic and extrinsic factors that affect it. The implications for wound healing and protection against potential pathogens or environmental conditions highlight a crucial role of skin homeostasis. Indeed, recent studies have identified associations between shifts in these commensal populations and physiological changes, such as aging and diverse dermatological diseases, not only in humans but in all vertebrates [5, 6].