ABSTRACT
The traditional view of the stratum corneum (SC) regards the outer layer of the epidermis to be relatively impermeable, highly resilient, and analogous to plastic wrap. This passive model, which holds that permeation is governed solely by the physical-chemical properties of the SC, dominates strategies for transdermal drug delivery. The permeability barrier forms coincident with the secretion of lamellar body contents at the stratum granulosum–SC interface. Numerous studies have described the changes in lipid composition that accompany SC formation in murine, porcine, and human epidermis. Epidermal lipid synthesis is both highly active and largely autonomous from systemic influences. The morphological basis of the aqueous pore pathway has been debated extensively, based on theoretical calculations of the molecular weight of compounds that traverse the SC and their respective activation energies. During the final stages of epidermal differentiation, a sequence of membrane transitions occurs within the SC extracellular domains.
