STUDY ON RELATIONSHIP BETWEEN HYDRATION LEVEL IN STRATUM CORNEUM, SEBUM LEVEL AND SKIN DRYNESS SENSATION: A case study on cheek of young male and female subjects in winter experiment

The purpose of this study was to investigate whether skin dryness sensation is based on the actual skin condition, for example, hydration level in stratum corneum. Subjective experiment had been carried out with the cooperation of sixteen young males and females. In experimental procedure, after subjects had been acclimated to ambient environment in test chamber room for over thirty minutes, they answered to questionnaire for evaluating ambient humidity condition and own body dryness condition. In addition, hydration level in stratum corneum, transepidermal water loss, sebum level and skin surface temperature on cheek were measured after questionnaire had been finished. In this paper, the analysis was performed targeting under the condition that subjects did not perceived sweating. The results and findings are listed below. 1) It was found that there is a significant partial correlation coefficient between hydration level in stratum corneum and cheek dryness sensation, if the sebum level was the same. 2) In male subjects, a significant correlation was observed between the hydration level in stratum corneum and cheek dryness sensation, regardless of sebum level. And although not significant, their hydration level in the stratum corneum showed a weak correlation with actual environmental humidity. 3) In female subjects, the dryness sensation on cheek was observed to have a significant positive correlation not with hydration level in stratum corneum but with sebum level. In addition, it was shown that the sebum level is an explanatory variable that can predict the dryness sensation on cheek well. Moreover, there was no significant correlation coefficient between sebum level and actual environmental humidity. 4) Cheek dryness sensation by female subjects was also strongly correlated with humidity sensation that is an evaluation index for environmental humidity. However, it was observed that there is no significant correlation between female humidity sensation and actual environmental humidity. Furthermore, humidity acceptability to environment showed a covariant relationship with sebum level. From the above, the smaller the hydration level in stratum corneum, the more the cheek dryness sensation tends to be evaluated as being "dry", under the stipulation of constant sebum level. However, female dryness sensation on cheek may depend on rather the sebum level than the hydration level in stratum corneum. As a result, the environment in which female subjects cl