In vivo evaluation of the stratum corneum barrier function in blacks, Caucasians and Asians with two noninvasive methods.

This study compared in man the in vivo barrier function of stratum corneum in three racial groups: black, Caucasian and Asian, by two noninvasive technics. They were transepidermal water loss (TEWL) determination measured with an evaporimeter and laser Doppler velocimetry (LDV) to measure the lag time before the vasodilation induced by application of methyl nicotinate (10 microliters of 0.5% solution in ethanol/propylene glycol 95/5 v/v). Both methods were performed simultaneously on each forearm of 7 black, 8 caucasian and 6 Asian subjects before and after removal of the stratum corneum by stripping. TEWL measurements were higher (p < 0.01) in Asians and Blacks compared to Caucasians. Stripping (8 or 12 strips) increased TEWL in all groups; TEWL increase percentage was higher (p < 0.05) in Asians compared to Caucasians. Vasodilatation lag times assessed by LDV showed that skin permeability was more important in Asians (p < 0.01) and in Caucasians (p < 0.05) than in blacks. Lag times decreased with stripping. After 8 or 12 strips, the order of sensitivity was: Asian > Caucasian > black. Our study showed that, with both noninvasive methods, removal of the stratum corneum increased permeability, with racial differences.