ABSTRACT
INTRODUCTION The stratum corneum (SC) is the outermost layer of the skin, and plays a principle role in maintaining the barrier function of the skin, regulating the evaporation of endogenous water from the body, and preventing the invasion of potentially harmful exogenous stimuli. The structure of the SC can be illustrated as a brick wall, consisting of dead corneocytes as the bricks and intercellular lipid lamellae as the mortar (1). Corneocytes, which are the final product of terminal differentiation of epidermal keratinocytes, have a polygonal, flattened shape, approximately 1-m thick and 50 m in diameter (2,3), and are piled up in 10 to 20 layers, depending on the anatomical site, although exceptionally, over 40 layers are stacked at the palm and sole (4). Corneocytes are linked together via cohesive protein complexes called corneodesmosomes, and their constituents, including desmocolin, desmoplakin, and corneodesmosin, are proteolytically degraded concomitantly with vertical movement toward the superficial layer of the SC, where they are finally exfoliated as their cohesiveness is destroyed (5).
