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 velocimetry (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 vasodilator drugs. The study was performed on untreated skin and after removal of the stratum corneum by 12 strips. The influence of molecular weight and solubility of different nicotinates (methyl, ethyl, hexyl and vitamin E) were also studied on 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. Moreover Asian skin was significantly more sensitive to stripping (P < 0.05) than Black skin. A significant shorter lag time was obtained with small and hydrophilic nicotinates (methyl and ethyl) (P < 0.01) compared to a lipophilic one (hexyl). The alteration of the stratum corneum barrier 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 determination of skin absorption.