Sugiyama, M., Itagaki, H., Katsumura, Y., and S. Kato. A Strategic Approach for Predicting Phototoxicity of Cosmetic Ingredients. ATLA. 1999. 27: 356.

Phototoxic skin reactions are caused by certain substances under light exposure. When they absorb photons and are activated, phototoxic chemicals can damage cell membranes, can damage cell organelles, or can interact with DNA. Many in vitro methods to predict phototoxicity, based on various mechanisms, have been developed and reported. We have validated three types of in vitro methods and a battery of assays to assess phototoxicity of cosmetic ingredients. The in vitro methods used were photohaemolysis testing of red blood cells (RBC), a technique to predict damage to cellular membranes, yeast growth inhibition assay, and the 3T3 mouse fibroblast neutral red uptake phototoxicity (3T3 NRU PT) test, a candidate for the OECD guidelines which estimates the effects on cell organelles. In comparison with the in vivo data in guinea-pigs, the yeast growth inhibition assay was the most correlated method. No false negatives were observed in the battery of the yeast growth inhibition assay and the RBC photohaemolysis assay. Because positive reactions were observed in a few chemicals only with RBC photohaemolysis or the 3T3 NRU PT test, it was suggested that a combination of methods based on different mechanisms would be needed for the safety assessment of phototoxicity of chemicals. Our results indicated that the battery of yeast growth inhibition assay and the RBC photohaemolysis assay is the most effective tool for assessing phototoxicity of ingredients. It was also noticed that the test methods should be selected with consideration of the physicochemical properties of the chemicals to be tested.