Water evaporation rates from a model of stratum corneum lipids.

Water evaporation rates were measured from thin samples of a model layered structure of stratum corneum lipids with 32% water. A model with only free fatty acids present gave the lowest evaporation rates, while a model with only oleic acid gave values approximately 50% higher. Using the total lipid spectrum of stratum corneum gave a structure with an evaporation rate between those mentioned above. The diffusion coefficients calculated were one to two orders of magnitude higher than those of stratum corneum, reflecting the influence of the proteinous part of the latter structure. A sample with only saturated fatty acids gave extremely high evaporation rates; in fact, they were of the same magnitude as those from an unprotected water surface.