Prediction of benzoyl peroxide phototoxicity by photoepidermotests after repeated applications. Preventive value of a UVB filter.

The predictive phototoxicity test known as photoepidermotest consists of twice daily applications of the product tested for 16 days, followed by total spectrum irradiation with a 2,500-W Xenon lamp in infraerythema and supraerythema doses. Phototoxicity is revealed by an erythema with the infraerythema dose and/or by accentuation of the erythema provoked by the supraerythema dose when compared with the "irradiation only" (i.e., no product) control skin area. This technique, used in a controlled, double-blind trial, showed that a 10% benzoyl peroxide (BPO) gel was phototoxic in eight out of 18 subjects tested (44%). It also showed that adding a UVB filter (phenylbenzimidazole sulfonic acid 1%) to the BPO preparation was effective in preventing phototoxic reactions in seven of these eight subjects.