British Journal of Dermatology (1989) 120, 787-794. Cutaneous reactive hyperaemia: racial differences induced by corticoid application E.BERARDESCA AND H.MAIBACH Department of Dermatology, University of California Medical School, San Francisco, CA 94143, U.S.A. Accepted for publication 29 December 1988 SUMMARY The postocclusive hyperaemic reaction before and after a single i h application of a potent corticoid (clobetasol 005",, in ointment) was recorded by means oflaser Doppler velocimetry in order to elucidate different racial responses in skin vasoconstriction. Fourteen young male subjects entered the study (eight Caucasians, six Blacks). Reactive hyperaemia was recorded after 4min of occlusion of the forearm bloodflow.The following parameters of the hyperaemic reaction were investigated: area under the curve response, peak response, rise of blood flow slope to peak and decay of blood flow slope after peak. Different responses were recorded in the Black subjects after the vasoconstrictive stimulus compared to the Caucasians, namely: decreased area under the curve response (P<004); decreased peak response (P<ooi); decreased decay slope after peak bloodflow(P < 004). These data are consistent with a different reactivity of blood vessels in black skin and possibly not related to the transcutaneous penetration of the chemical compound. The vasoconstriction assay is widely used to assess the transcutaneous penetration of corticoids. This technique, developed by McKenzie and Stoughton,' is based on the ability of glucocorticoids to elicit a blanching reaction after topical application. The degree of vasoconstriction usually parallels the anti-inflammatory effect. The blanching reaction is usually scored visually, rendering this technique sensitive to subjective evaluation. The non- invasive, objective quantification of skin blood flow was demonstrated in a preliminary report, to be ineffective in monitoring and quantifying corticoid induced vasoconstriction.^ To overcome these problems and allow an objective evaluation of blanching, Bisgaard et aP recorded, by means oflaser Doppler velocimetry, the reactive hyperaemia induced by arterial occlusion. Reactive hyperaemia is the temporary increase of bloodflowin a tissue when the circulation is released after a period of vascular occlusion. Two theories have been advocated to explain this phenomenon: the myogenic and the metabolic theory. The former, introduced early this century,** reflects the concept that arteries and smooth muscles react to stretching by contraction Correspondence: Dr E.Berardesca, Department of Dermatology, University of Pavia, IRC.CS Policlinico S.Matteo, Pavia, Italy. 787