[Phototoxic activity of 5% benzoyl peroxide in man. Use of a new methodology]

In order to conform to the conditions in which a 5% benzoyl peroxide compound is being used, a new methodology has been developed and applied to 24 volunteers: photobiologic tests were performed and UVB irradiation at infra- and supra-MED times of exposure as well as UVA irradiation on usually covered and usually uncovered areas, after single and multiple applications. This double-blind study (vehicle alone and active substance alone) has been carried out in each subject. UVB phototoxicity resulted in the occurrence of an erythema for an infra-MED time of exposure and/or in changes in the erythema as compared to an adjacent control area for the supra-MED time of exposure. This was found in 8 patients (33%), only on repeatedly irradiated areas, but never with the vehicle alone. No UVA phototoxicity was evidenced. This study confirms the possible phototoxic action of benzoyl peroxide after UVB exposure. It emphasizes the usefulness of repeating the applications on both covered and uncovered areas in photosensitivity tests of a substance.