ABSTRACT
INTRODUCTION Epidermis, the uppermost, multilayered epithelial compartment of the skin, provides an efficient barrier for the body against physical, chemical, and microbial agents, and is necessary for survival in a terrestrial environment. This protective function is mainly achieved by the outermost layer of the epidermis, the cornified layer or stratum corneum (SC). This layer is composed of corneocytes, which are dead and flattened “mummified” cells endowed with a cornified envelope that provides extreme individual resistance. Corneocytes are strongly bound to each other by corneodesmosomes, the only described intercellular junctions of the SC, derived from the desmosomes of the granular keratinocytes. Altogether, corneodesmosomes and corneocytes constitute the SC, which provides a mechanical protection to the epidermis and plays an essential role in the barrier between the human body and its environment. A lipid matrix organized as lamellae, in which corneocytes are embedded, is also essential to the barrier function, mainly through its prevention of water loss. In the upper SC, the controlled rupture of the corneodesmosomes leads to the desquamation process, that is, to exfoliation of single corneocytes from the epidermal surface.
