POLYMORPHISM IN STRATUM-CORNEUM LIPIDS

Fourier transform infrared spectroscopy (FTIR) was employed to investi gate the thermotropic phase behavior of stratum corneum lipid multilam ellae. Stratum corneum (SC), the uppermost layer of mammalian skin, is unusual in many respects. It has been demonstrated that the lipids of the stratum corneum provide the primary electrical and transport resi stance in the skin. These lipids are unusual in their composition, str ucture and localization; they contain only cholesterol, fatty acids an d ceramides and they form broad, multi-lamellar sheets which are locat ed extracellularly. The FTIR results from both the symmetric CH2 stret ching and the CH2 scissoring vibrations suggest that the SC lipids exh ibit polymorphic phase behavior below the main phase transition temper ature. The multiple phases are most likely crystalline mixtures of dif ferent alkyl chain packings, along with solid-liquid phases. Similarit ies between the FTIR results reported here for SC lipids and those obt ained for cholesterol-containing gel phase phospholipids suggest that the non-uniform distribution of cholesterol occurs in each system.