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.

The origin of alkanes found in human skin surface lipids.

Lipids extracted from human skin contain variable amounts of paraffin hydrocarbons. Although the composition of these alkanes strongly resembles petroleum waxes, it has been proposed that they are biosynthetic products of human skin. To investigate this question, skin surface lipids from 15 normal subjects were analyzed for the amount and composition of alkanes, using quantitative thin-layer chromatography and quartz capillary gas chromatography. The alkanes were found to constitute 0.5% to 1.7% of the skin lipids. Subjects differed greatly in the chain length distribution of their alkanes between 15 and 35 carbon atoms, and in the relative amounts of normal alkanes (like those in petroleum waxes) and branched chain alkanes (like those in petroleum lubricating oils). In 6 subjects, the alkane content of cerumen from each ear was examined to investigate whether alkanes arrive at the skin surface by a systemic route or by direct contact with environmental surfaces. No trace of alkanes was found in 11 of the 12 cerumen samples. Using a tandem accelerator mass spectrometer for carbon-14 dating, a combined sample of the skin surface alkanes was found to have a theoretical age of 30,950 years, similar to that of a sample of petrolatum. These analyses indicate that the alkanes found on the surface of human skin are mixtures of a variety of petroleum distillation fractions that are acquired by direct contamination from the environment.