Structure and function of the epidermal barrier

The skin is divided into 2 main structural layers: the epidermis and the dermis. The epidermis is generally considered to be subdivided into 5 separate strata: basal, spinous, granular, lucid, and corneum. The vital barrier function of the skin resides primarily in the top stratum of the epidermis, the stratum corneum (SC). The SC is the barrier to the passive diffusion of water out of the skin, allowing us to live in air without suffering from dehydration, and is the barrier to other molecules including irritants into the skin. The epidermis also has immunologic functions and provides some protection of the skin from ultraviolet light via the pigment system. This paper will review the structure and function of the epidermal barrier and the response to environmental challenges such as repeated handwashing. Emphasis will be placed on the SC, the front line of the skin's defense against the insults of the outside world.