IN-VIVO DIFFERENCES BETWEEN ASIAN, BLACK-AND-WHITE IN THE STRATUM-CORNEUM BARRIER FUNCTION

The stratum corneum barrier function of Blacks, Caucasians and Asians were compared in vivo. A noninvasive technic, laser doppler velocimetr y (LDV), was used to evaluate the cutaneous penetration of nicotinates by the determination of the lag time before vasodilatation induced by the application of those local vasodilatator drugs. The study was per formed on untreated skin and after removal of the stratum corneum by 1 2 strips. The influence of molecular weight and solubility of differen t nicotinates (methyl, ethyl, hexyl and vitamin E) were also studied o n Japanese skin. Vasodilatation lag times assessed by LDV, with methyl nicotinate (MN), showed that skin permeability was more important in Asians (P < 0.01) and in Caucasians (P < 0.05) than in Blacks. Moreove r Asian skin was significantly more sensitive to stripping (P < 0.05) than Black skin. A significant shorter lag time was obtained with smal l and hydrophilic nicotinates (methyl and ethyl) (P < 0.01) compared t o a lipophilic one (hexyl). The alteration of the stratum corneum barr ier function by stripping showed a more important modification with MN (P < 0.05) than with hexyl nicotinate. Consequently, this noninvasive method can evaluate the modifications of the stratum corneum barrier function and racial origin has to be taken into account in the determi nation of skin absorption.