Photomaximization test for identifying photoallergic contact sensitizers.

The photomaximization procedure was designed to identify topical photocontact sensitizers following the format of the maximization test for contact sensitizers. The test agent is applied for 24 hours followed by exposure to three Minimal Erythema Doses (MED) of solar simulated radiation twice weekly for 3 weeks (six exposures) in a panel of 25 white Caucasoids. The subjects are challenged 2 weeks later with 4.0 J/cm2 of long-wave ultraviolet radiation (UV-A). Photocontact sensitization was induced to 3,3'4',5-tetrachlorosalicylanilide (TCSA); dibromosalicylanilide (DBS) but not to tribomosalicylanilide unless the latter was contaminated with DBS. Jadit and bithionol were weak photoallergens. The highest rate of sensitization was given by 6-methylcoumarin, a widely used synthetic fragrance. Hexachlorophene and trichlorocarbanilide were negative.