1. Gut-Skin Axis: Role in Health and Disease

The human microbiome includes microorganisms and their cumulative genetic details that reside in the human body. Skin, the body’s most external organ and exposed to the external environment, is an ecosystem with 1.8 m² area. It has a varying epidermal thickness, folds, and appendages in different areas including along with varying moisture and temperature level on the skin surface. Microbial colonization on the skin surface starts from the time of birth. The mode of delivery affects the colonization process to a considerable extent. The group of microbes colonizing the skin surface is determined by physical and chemical features of it, which applies to microbes inhabiting the gut and other ecological niches in the body as well. There is several common important characteristics shared commonly by gut and skin, where both are (1) heavily vascularized, (2) richly perfused, (3) densely innervated, (4) integrated to the immune system, (5) highly associated with the endocrine system, (6) extensively colonized with recognizable microbiota, and (7) both helps our body to communicate with its external environment. It has variously been reported that a close and bidirectional association within the gut and skin in maintaining the homeostasis and allostasis of skin and also gastrointestinal (GI) health. Therefore, numerous intestinal pathologies have been linked to skin comorbidities. It has been found that skin is directly impacted by the various circumstances that principally affect the intestine. Similarly, various gastrointestinal disorders could be linked to distinct dermatological entities. In the same context, a growing body of proof proposes an association of intestinal dysbiosis with many regular inflammatory skin pathologies including atopic dermatitis (AD), psoriasis, rosacea, and acne vulgaris. And the realization of this interconnected association between skin and gut has resulted in a new concept of the “Gut-Skin Axis.” An intimate bidirectional engagement between the gut and the skin has been well established by growing research evidence in this domain. Recent reports have indicated that the administration of specific Lactobacilli strains to mice can significantly alter the overall skin phenotype. Despite increasing research efforts in this domain, a systematic investigation of the “Gut-Skin Axis” remains ill explored by both gastroenterology as well as dermatology researchers. And in this context, here we are discussing various aspects of the Gut-Skin Axis and its role in the general well-being of individuals.