Synopsis

The outer externally facing stratum of human epidermis, the stratum corneum (SC), provides a robust and effective permeability barrier which, by regulating water loss, makes human life on earth possible. Over 1200 ceramide species have been identified in human SC, complementing our understanding of the composition of free fatty acids and cholesterol derivatives, which together constitute the SC’s lipid matrix. The permeability barrier function of skin ultimately derives from the inter- and intra-molecular organisation of SC lipids. Recent studies have reported changes in SC lipid composition and molecular organisation associated with skin diseases, environment stresses, lifestyle, and life-stage. Our own studies have shown differences in skin barrier organisation with body site and skin depth. Whilst orthorhombic packing of SC lipids is critical to healthy skin barrier function, we do not observe such lipid packing in the much thinner SC of face skin. No doubt, this is one contributing factor to the reduced barrier function of face skin.  Regardless of body site, a robust fast recovery of barrier function is essential to skin health. As such, the skin’s response to external chemical or physical stresses is one important measure of healthy skin. For example, a characteristic of older skin is a delayed or incomplete barrier recovery following external stress. In recent work we have quantitatively measured the restoration of inter- and intramolecular SC lipid organisation following thermal perturbations equivalent to those encountered in skin cleansing. Our results indicate lipid organisation remains perturbed for over 24 hours following a thermal stress. In addition to an overview of our current understanding of SC lipid composition and organisation, this presentation will describe some results from our own studies illustrating the importance of SC lipid organisation to healthy skin.