Contact photoallergy testing of sunscreens in guinea pigs

The potential of 3 sunscreens (p-aminobenzoic acid, 4-isopropyldibenzoylmethane and homosalate) and 2 known human photoallergens (musk ambrette and tetrachlorosalicylanilide) to cause photoallergy, phototoxicity, and/or contact sensitization was determined using a guinea pig photoallergy model, as previously described by Harber and associates. The model was slightly modified by employing 6 exposures over 2 weeks and using Hill Top Chambers for application of the test material. Contact photoallergy was detected in guinea pigs treated with musk ambrette or tetrachlorosalicylanilide (TCSA), although with TCSA, a lower incidence of contact sensitivity and phototoxicity was also detected. The results of studies conducted with sunscreens showed that p-aminobenzoic acid was photoallergenic, whereas homosalate and 4-isopropyl-dibenzoylmethane (Eusolex 8020) were not. However, contact sensitization, and to a lesser degree primary irritation, was detected with Eusolex 8020 at the concentrations employed in this study. The results of these studies suggest that this guinea pig model is a suitable model for assessing the photoallergic potential of various compounds, including the sunscreens tested in this study.