Suppression of Sebum Secretion with 13-cis-Retinoic Acid: Effect on Individual Skin Surface Lipids and Implications for Their Anatomic Origin

The contribution of the keratinizing epidermis to the human skin surface lipid film has been difficult to ascertain because, after its release from the epidermal cells, epidermally derived lipid inevitably becomes mixed with sebum. In the present study, the sustainable rates of production of the 5 neutral lipid classes found on the skin surface (triglycerides + free fatty acids, wax esters, cholesterol, cholesterol esters, and squalene) were measured on the foreheads of acne patients before, during, and following treatment with 13-cis-retinoic acid, a drug which suppresses sebum production profoundly. Since sebum production was high in the patients before treatment and was suppressed to a few percent of the pretreatment level in some of the patients during treatment, data covering a wide range of sebum production rates were obtained. By using squalene as a measure of sebum production and plotting the rates of production of the other lipid classes vs the rate of production of squalene, it was possible through extrapolation to estimate the residual (i.e., epidermal) rate of production of each lipid class at zero sebum production. The results indicated that epidermis releases triglycerides + free fatty acids and cholesterol to the skin surface. The cholesterol esters in freshly secreted skin surface lipids appeared to be almost entirely sebaceous in origin. Measurements were also made of the percentages of cholesterol esters in lipid collected from the scalp after several days' accumulation and were compared to corresponding values for the forehead lipid. The percentages of cholesterol esters in scalp lipid tended to rise when sebum production was suppressed by the drug, rather than remaining relatively constant as occurred in the freshly secreted forehead lipid. This result indicated that epidermis may contribute to skin surface cholesterol esters, probably through skin surface esterification of epidermal cholesterol