Figure 3.

Gut-skin axis in a homeostatic state: The gut environment provides niches for gut microbiota with nutrients and optimal growth conditions, while gut microbiota carry out pleiotropic functions in maintaining body homeostasis. Microbial metabolites, for example, short-chain fatty acids, secondary bile acid, and several small molecules, not only locally maintain enterocyte functions but also exert systemic effects, including immune tolerance. This effect is linked to the skin via blood circulation, forming the so-called “gut-skin axis,” and provides an anti-inflammatory environment in the skin, optimizing interactions with skin microbiota. Skin microbiota in a homeostatic state help prevent pathogen colonization, modulating local immune responses and facilitating wound healing. Transient external perturbations, either cutaneous or mucosal, could disrupt microbiota composition, resulting in a transient dysbiosis state. The balanced microbiota could be recovered by perturbation removal, growth promotion of microbiota by proper diets, and, although in development, intervention with pro-and prebiotics. (Created with BioRender.com) (accessed on 12 May 2022). Abbreviation: pH, potential of hydrogen; UV, ultraviolet.