Evolution of Skin Barrier Science for Healthy and Compromised Skin

Abstract

Skin is a complex organ comprised of multiple cell types and microstructures that work in concert to serve critical functions and support the body’s homeostasis. It is the outermost, cornified layer of our body that is primarily responsible for the permeability barrier, protecting against external aggressors and preventing water loss from within. The understanding of the organization, functionality, and underlying mechanisms of the skin barrier has evolved greatly through the years. The formation of an intact and well-maintained stratum corneum (SC), where the permeability barrier resides, relies heavily on the differentiation of epidermal keratinocytes and the synthesis, release, localization, and binding of lipids that include principally ceramides, cholesterol, and free fatty acids. The in-depth research on SC barrier, its disruption in the pathogenesis of diseases, as well as on barrier responses to environmental insults, has enabled the development of modern therapeutics and topical care routines. Among them, ceramide-containing moisturizers have clinically demonstrated the ability to support the management of skin conditions such as atopic dermatitis and psoriasis by reducing the disease severity and recurrence and improving the patients’ perception of overall skin quality and health. This review focuses on the contributions of various barrier constituents to skin barrier function in health and pathological conditions, and how topical interventions containing essential barrier lipids support barrier restoration and provide relief.