Screening of Cosmetics Ingredients for Phototoxic Potential Using the In Vitro 3T3 Neutral Red Uptake Phototoxicity Test
Phototoxicity is an acute toxic response after exposure to a phototoxicant and either UV radiation or visible light (UV/VIS). Phototoxicity from substances applied topically typically occurs at the site of photo-irradiation. Phototoxicity is the result of direct cellular damage caused by a non-immunological inflammatory response. Clinically, phototoxicity resembles an exaggerated sunburn (erythema, increased skin temperature, pruritis and edema). Phototoxicity reactions have been reported for both synthetic substances and those which occur naturally (e.g., botanical extracts). Although symptoms generally subside quickly, the potential for substances used in topical products to cause phototoxicity is clearly of concern for manufacturers of cosmetics, personal care and other consumer products. Historically, the potential to cause phototoxicity from substances applied topically was evaluated by utilizing various animal models. However in 1997 the 3T3 Neutral Red Uptake Phototoxicity Test (3T3 NRU PT) was validated by ECVAM’s Scientific Advisory Committee as an in vitro method for evaluating the phototoxic potential of chemicals shown to absorb in the UV/VIS range. To illustrate the utility of the 3T3 NRU PT as a useful screening tool in the safety evaluation of potential cosmetic ingredients, the results of the evaluation of 42 botanical extracts and 25 synthetic chemicals found to absorb in the UV/VIS range are reported. Most substances evaluated were found not to be phototoxic in vitro; however, 9 substances were identified as potentially/probably phototoxic in the 3T3 NRU PT and were eliminated from further consideration for use as cosmetic ingredients. Several substances found to be non-phototoxic in the 3T3 NRU PT were formulated with other ingredients in a prototype cosmetic formulation and subject to clinical testing. No manifestations of phototoxicity were observed in any of the test subjects in the prototype formulation containing any of the substances identified as non-phototoxic in vitro.