Equilibrium water sorption in human stratum corneum.

The water content of the stratum corneum (SC) is a key factor in skin barrier homeostasis; it is intimately related to both skin condition and skin permeability. Studies of water uptake in excised human SC show strong similarities and allow characterization of the equilibrium SC water sorption isotherm in terms of widely used theoretical models. At low water activities, SC water sorption resembles that in other keratinized tissues (i.e., wool and horn), whereas at high water activities, it resembles that in polymeric hydrogels. In this paper, theoretical water sorption models [Brunauer-Emmett-Teller (BET), D'Arcy-Watt, and Frenkel-Halsey-Hill] are fit to the combined human SC water sorption data from our laboratories and others. Each of these models provides a satisfactory description of the equilibrium water content of human SC over the water activity range 0.03-1.0. An accompanying paper discusses the implications of SC water sorption on water mobility in corneocytes and on SC permeability.