Double approach to improve epidermal barrier function

It has been recently accepted that, in addition to the stratum corneum, intercellular junctions – and, especially, tight junctions (TJs) – also play a role in homeostasis of the skin barrier function1,2 by ensuring cohesion between the keratinocytes of the stratum granulosum, and secondly, by regulating epidermal Ca2+ gradient and polarised lipids bodies transport.3 This article tackles a double approach for improving the epidermal barrier function by increasing the dynamic flow of lipids and by stimulating cohesion of the epidermis.

 The primary function of the skin is to act as a barrier against unwanted influences from the environment and to protect the body from water loss. This barrier function is ensured mainly by the stratum corneum, the upper layer of the epidermis. The stratum corneum comprises corneocytes, which are keratinised keratinocytes, surrounded by lamellar lipid membranes. These lamellar lipids play a fundamental role in the structure and functions of the epidermis. They cement the corneocytes and with them form the permeable barrier of the epidermis. Their particular composition – ceramides (50%), cholesterol (25%) and long-chain free fatty acids (15%) – and their arrangement in lipid bilayers in the intercorneocyte space determine the functional characteristics of the skin barrier.4 It has been recently accepted that, in addition to the stratum corneum, intercellular junctions – and, especially, tight junctions (TJs) – also play a role in homeostasis of the skin barrier function.1, 2 Indeed, TJs ensure cohesion between the keratinocytes of the stratum granulosum by forming a selective semipermeable barrier preventing water and solutions from “leaking” out towards the surface of the skin via the paracellular space. Secondly, recent investigations showed that TJs mediate the epidermal Ca2+ gradient and polarised lamellar bodies transport, and thus influence the formation of the stratum corneum barrier function.3 Today, one of the main concerns of the cosmetic industry is to provide skin care with a restructuring and moisturising effect. Considering the preponderant role of lipids and TJs in the homeostasis of the barrier function, we propose a double approach with natural active ingredients enabling the improvement of the epidermal barrier function by targeting these biological processes (Fig. 1).

Target 1: flow of lipids