Studies on the chemical composition of human epidermal lipids.

Detailed examinations have been made of the skin surface lipids and the lipids of the hair surface from human subjects (1, 2). These materials arc a mixture of indefinite proportions of sebum together with lipids derived from the keratinizing cells of the epidermis. Furthermore, the constituents of scbum or of the cpidermal lipids proper may be altered before or after they reach the surface. Glycerides of sebum, for instance, are probably split in the sebaceous duct or follicle neck (3) and cholesterol appears to be esterified while it is carried to the surface of the keratinizing epidermis (4, 5). It is therefore of considerable interest to analyze the cpidcrmal lipids as they occur in the Malpigbian layer because they may be altered in transit to the surface and may also be diluted by admixture with scbum. Such determinations were carried out earlier on plantar epidermis (5), and more recently on separated total epidermis from the back by Glasenapp and Lconhardi (6) and from the forearm by Nicolaides and Rothman (7). Previous work has been limited because of the very small amounts of lipid available for analysis. In the present study a total of 701 mg. of cpidermal lipids was obtained from 43 individuals (equivalent to about 500 sq. in. of skin). This is still too small for detailed ana]ysis using conventional methods, but the development of newer methods of lipid analysis, in particular the application of gas chromatography (8), has enabled a relatively detailed analysis of the component lipids to be made with this amount of material.