The effect of accumulated lipids on measurements of sebum secretion in human skin.

When sebum is collected from the skin surface in an absorbent material, the amounts obtained in successive collections at the same site decline steadily. In the present study, sebum was absorbed into bentonite clay applied to 2.5 sq cm areas on the foreheads of 3 subjects for 3-hr intervals during 24 hr. The amounts of sebum obtained, measured by thin-layer chromatography, declined for 12 hr and then remained constant for the remaining 12 hr. It was inferred that the final, sustainable rate represents the true rate at which sebum was being secreted by the sebaceous glands, and that the additional sebum collected at earlier intervals was obtained from an accumulation in the stratum corneum or in the follicular canals. For the 3 subjects, the accumulated sebum averaged 213 micrograms/sq cm, compared with a sustainable secretion rate of 25 micrograms/sq cm/hr. The large quantity of accumulated sebum, relative to the secretion rate, could obscure differences between subjects when sebum secretion rates are measured by short-term collections of sebum in absorbent materials.