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The phase properties and structural characteristics of stratum corneum (SC) lipid lamellae have been a subject of considerable interest. To clarify the individual role of the stratum corneum constituent lipids, such as ceramides, free fatty acids, and cholesterol, we investigated the thermotropic properties and aggregation structures of a pseudo-ceramide/stearic acid (1/1 mole ratio)-cholesterol system, which is a simplified model for the natural lipids. Differential scanning calorimetry (DSC) detected decreases of melting entropies (delta Sm) by the incorporation of cholesterol into both anhydrous and hydrated equimolar mixture of pseudo-ceramide (SLE) and stearic acid. Moreover, there was a linear relationship between the cholesterol content and the melting entropies in the region of 0-33 mol% cholesterol for both the anhydrous and hydrate lipids. In addition, as the concentration of cholesterol increased, a liquid lateral packing (4.5 A) appeared in the wide-angle X-ray diffraction and the intensity of a hexagonal packing (4.15 A) decreased. The results from the present study strongly follow the idea that cholesterol can regulate the mobility of hydrocarbon chains of the natural stratum corneum lipid bilayer, which is primarily responsible for the barrier properties.