Changes in the relative amounts of endogenous and exogenous fatty acids in sebaceous lipids during early adolescence

Skin surface lipid samples were collected from the scalps of 40 males, aged 9-15, and the lipid class composition of each was analyzed by quantitative thin layer chromatography. The ratio of wax esters/[cholesterol + cholesterol esters] (WE/[CH + CE]) increased with age. The wax ester, cholesterol ester, triglyceride, and free fatty acid classes were isolated from each sample and the fatty acid compositions were determined by capillary gas chromatography of fatty acid methyl esters (FAME) prepared from each lipid class. The concentrations of most of the different types of fatty acids were found to be correlated with the WE/[CH + CE] ratio. Those straight chain fatty acids that are thought to be synthesized mainly within the sebaceous glands, such as 14:0, 14:1, 16:1, and 18:2 delta 5, 8 tended to increase with increasing WE/[CH + CE], while fatty acids which circulate in the blood, such as 18:0, 18:1, and 18:2 delta 9, 12, tended to decrease with increasing WE/[CH + CE]. For the majority of straight chain fatty acid types, the data could be fitted to the equation y = a + b/[x + 1], which can be derived from simple assumptions concerning the origins of the various sebum components. The FAME from the wax esters were separated into saturated and monounsaturated fractions and analyzed by capillary gas chromatography to determine the concentrations of the different types of branched chain FAME present. In the wax esters, straight chain fatty acids tended to increase with increasing WE/[CH + CE], while terminally branched (iso and anteiso) fatty acids tended to decrease. Other branched chain fatty acids increased up to a WE/[CH + CE] ratio of about 2 and then decreased at higher ratios.