Composition of cerumen lipids.

Lipids were extracted from "wet" cerumen and analyzed by quantitative thin-layer chromatography to determine their composition. The lipid fraction comprised 52% of the dry weight of cerumen and consisted of squalene (6.4%), cholesterol esters (9.6%), wax esters (9.3%), triacylglycerols (3.0%), fatty acids (22.7%), cholesterol (20.9%), ceramides (18.6%), cholesterol sulfate (2.0%), and several unidentified polar components (7.5%). In addition to the extractable lipids, the residue contained an additional 0.9% lipid that could be released only after saponification. This covalently bound lipid consisted of two unusual ceramides (63.4%), omega-hydroxyacids (27.7%) and nonhydroxy fatty acids (8.8%). The composition of this bound lipid resembled that recently found in human stratum corneum, which is thought to comprise a lipid envelope on the outer surface of the corneocytes. The free and covalently bound lipids may be significant determinants of the properties of cerumen. Desquamation of corneocytes and their associated lipids from the epidermal lining of the ear canal may make a major contribution to cerumen.