Changes in skin surface lipid composition induced by severe caloric restriction in man.

Lipid collected from the surface of the human forehead is predominantly (-95%) the product of the sebaceous glands (1) and contains on the average 41 % triglycerides, 16.5% free fatty acids, 25% wax esters, 12% squalene, 1.5% cholesterol, 2% cholesterol esters, and 2% diglycerides (2). This sebum composition shows little variation between normal subjects or over long periods of time in individual subjects, except for the degree of hydrolysis of triglycerides to free fatty acids effected by bacteria (3). We reported previously, however, that the proportion of squalene in this mixture increases markedly in obese subjects undergoing prolonged total fast for weight reduction (4). This change resulted from suppression of the synthesis of all sebum constituents other than squalene, the production of which remained essentially constant. We now have evidence that a similar change in the composition of sebum occurs in normal nonobese subjects under essentially fasting conditions.