ABSTRACT
The principal role of the nucleated layers of the epidermis in terrestrial mammals is
to form a protective layer, the stratum corneum (SC), which interfaces with a
potentially hostile, desiccating external environment. This outermost layer
subserves a large set of distinct, defensive, or protective functions, serving not
only as regulator of permeability barrier homeostasis but also a large set of other
defensive functions (Table 1). Implicit in this set of functions is an emerging
awareness that the SC, though anucleate, possesses a wide array of metabolic
activities (concept of the “living stratum corneum”), and it is also now becoming
apparent that the outer epidermis is the initial sensor of changes in osmotic
pressure, pH, and thermal stimuli, serving as a critical environmental “biosensor”
(Table 2).
