Understanding the Complexities of the Stratum Corneum: Considerations and Strategies for Skin Barrier Maintenance Continuing Education Article Series

As the rst point of contact with a potentially drying external environment, the primary function of the stratum corneum (SC) is to limit evaporative water loss from the aqueous interior. Yet this is just one of many functionalities conferred by this unique barrier, also protecting against mechanical insults, the assault of foreign chemicals, and microorganisms, and even serving as the rst inherent defense against ultraviolet radiation. Beyond barrier function, the stratum corneum acts as a biosensor, reacting to and mobilizing as a result of both external and internal changes in order to maintain homeostasis and ultimately wear its multiple aforementioned hats. Since the stratum corneum is so profoundly responsible for maintaining healthy skin, there has been signi cant motivation to bet- ter understand the mechanisms through which it protects the viable epidermis from offending agents, as well as elucidate the way in which the SC ensures adequate hydration in order to enable proper epidermal enzyme function and tactile perception. Much of our understanding of the stratum corneum’s functional structure is derived from various disease states in which key SC elements are dysfunctional or absent, thereby providing the impetus for utilizing said components or derivations thereof in a wide range of products. In the article by Lee and Friedman, the biology of the stratum is reviewed to provide the framework for translational thera- peutic indications.To better appreciate the impact of primary skin disease on barrier stability and functionalities and what strategies to consider, Jordan and Baldwin identify speci c alterations in the stratum corneum in the setting of Acne Vulgaris, both inherent and iatrogenic resulting from use of therapeutics targeting said skin disease. Lastly, Schwartz and Friedman breakdown the various categories and ingredients used in moisturizers and barrier repair devices with the epidermal biology in mind to help the reader identify which elements are important for maximum impact. Targeted and personalized therapies don’t just have to be small molecule inhibitors and biologics – selecting even over the counter products based on their biologically relevant ingredients ts this popular and modern approach. Herein this supplement, we provide the tools to join the club.