THE QUANTITY AND VARIATION OF HUMAN SURFACE LIPIDS

Abstract

Human skin surface is covered with surface film. This film is said to have some protective functions and is assumed to be one of the important factors affecting skin surface condition. Since sebum is the main component of this film, in order to investigate the relationship between physiological condition of skin surface and skin type, we studied the variations in the amount and composition of sebum with respect to the age as well as the diurnal variation in the sebum excretion rate.
Sebum was collected by the method of Pochi et al and its components were analyzed with gas-liquid chromatography. The amount of sebum was calculated by the formula: Y=0.114x+2.03 where Y is the amount of squalene, X is that of total lipid. The rhythms of sebum excretion rate were analyzed by the least squares method and cosinor method.
The results obtained were as follows. Among the women between 18 and 40 years old the amount of sebum excretion from the forehead was nearly constant. For women over 40 years old the amount of sebum from trom the forehead began to decrease with the age. The total amounts of sebum varied widely in women with the average value of 71μg/cm. The composition of sebum also varied widely in women, especially in the composition of triglycerides. The average composition of sebum varied insignificantly with respect to the age and the amount of excretion sebum. The amount of replacement sebum exhibited diurnal variation. The sebum excretion rate from the forehead exhibited a circadian rhythm in both men men and women. The sebum excretion rate from the chest of men also exhibited a circadiadian rhythm. The excretion rates of sebum components squalene, wax esters and triglycerides, were synchronous. In the majority of subjects, the maximum sebum excretion was observed in the early morning. Although the wave form of sebum excretion rate was found to be composed of multiple rhythmic components of different frequencies (infradian and ultradian rhythms), this circadian rhythm was the main component of the sebum excretion rate rhythms.
The results show that both the amount of replacement sebum and the sebum excretion rate vary constantly with time. From this study, it is clear that the amount of sebum present on the skin varies significantly with the excretion rate rhythms and that this relationship must taken into consideration when investigating the condition of skin surface or characterizing the skin type.