The morphology and friction coefficient associated with water content and lipid on the skin of the inner part of the forearm, were investigated in 250 healthy subjects. It was found by electron microscopy that skin surface exhibited a pattern formed by two types of stripes, main stripes and fine stripes and these differ in length and depth from the superficial surface of the skin. Total length of the stripes on the skin surface per unit area decreases gradually with age of subject, and the pattern of the skin surface in advanced age is mainly formed by the main stripes. Friction coefficient of the surface depends largely on the total length of the stripes per unit area. It increases monotonically with the decrease of the total length.
The relationship was investigated between water content and friction coefficient on skin surface, and it was found that there was an optimum water content to minimize friction coefficient of the skin surface.
