Comparative study of the hydration of the stratum corneum between four ethnic groups: influence of age.

BACKGROUND: Several recent overviews have reported that significant work remains to be performed to understand and quantify the ethnic differences in skin properties. In this way, we have carried out a set of in vivo biophysical experiments on the skin of American women from different ethnic populations living in the same environment. Inter- and intraethnic skin micro relief results were already published, skin hydration differences are now reported here.
METHODS: The skin water content was evaluated taking advantage of the new skin capacitance imaging technique which allows to study stratum corneum hydration without suffering of the influence of the skin micro-relief and hair on the measurement. Three hundred and eleven American women from four ethnic groups were enrolled in this study. The investigation was performed during the summer season of 2004 on the major relatively distinct ethnic groups of Chicago, which is to say: African American, Chinese, Caucasian and Mexican. The hydration of the skin was investigated on the dorsal and ventral forearm sites as a function of ethnicity and age.
RESULTS: Skin dryness is higher on sun exposed sites for lighter skin tones, such as in Chinese and Caucasian women, than on sites that are primarily out of the sun; while, no skin dryness differences are seen on either site for African American and Mexican women whose skin is darker. The skin dryness does not change as a function of ethnicity for the younger group for either the ventral and dorsal site of the forearm. With age, however, the dryness of the skin is higher for African American and Caucasian women than for the two other ethnic groups, with a higher percentage increase in Caucasian women.
CONCLUSIONS: This study has revealed that the hydration of the skin is different according to ethnicity and that the age effects are influenced by ethnicity, suggesting anatomical or physiological property differences in ethnic skin. This study has also pointed out that the SkinChip seems to be a convenient and fast way to investigate both the micro relief as previously published and the dryness of the skin on a large number of subjects, and in this way will be very useful to improve our knowledge about skin of people from different ethnic groups and helping to develop specific products that are customized to all these populations.