The stratum corneum barrier: the final frontier.

The stratum corneum (SC) is the differentiated end product of the mammalian epidermis. It is vital to constancy of the milieu interieur (the environment within) because it prevents water loss and the penetration by potentially toxic xenobiotics, damaging radiation, and pathogenic microbes. The intercorneocyte space contains complex nonpolar lipids that constitute the water barrier. The formation of the SC in the process of keratinization is complex providing multiple opportunities for disorders to arise. The final act of keratinization is desquamation and for this to occur the controlled release of single corneocytes is required in which proteases play an important role. Tests and techniques are described that measure the structure and function of the SC.