Sebum Excretion. Methods of measurement and influence of physical factors.

Summary Sebum excretion is the entire feature which governs sebum outflow to the skin surface through follicular pore. It can be measured by numerous methods, the first of which, devised by Emanuel in 1936, was a solvent extraction followed by desiccation and weighing. At present, virtually the only methods used are the gravimetric and photometric ones. The first one, using absorbent paper to collect the sebum, was introduced by Strauss and Pochi, and improved by Cunliffe and Shuster. Schaefer and Kuhn-Bussius' photometric method is about as accurate as the previous one, but more simple and more rapid to use. Two parameters can be used to quantify sebum excretion: one static, the casual level (CL), i.e. the skin surface lipid amount of a non protected area neither wiped nor washed; the other is dynamic, the sebum excretion rate (SER), i.e. the skin surface lipid flow of a previously cleaned area. The significant differences of these values between different sex and/or age matched groups, give an account of the various stimulation levels of the sebaceous glands according to the underlying endocrine state. Several attempts have been made to show a sebum excretion regulation. Unfortunately, because of the divergences of their results, there is still no definite evidence of such an event occuring. Numerous experiments have also been carried out on the effects of skin temperature and sweat on sebum excretion. The first of these two parameters can act upon sebum skin surface spreading by changing sebum viscosity. The second one can modify local surface tension. Finally, the existence of a circadian rhythm constitutes a further parameter which must not be neglected when interpreting investigations of sebum excretion.