A screen for photoirritants in cultured cells.

Adverse photoirritant or photoallergic reactions may be caused by the interaction of certain chemicals with light. The behaviour of 20 chemicals (of which 12 were known UV absorbers and photoirritants, four were known UV absorbers and non-photoirritants and four were known non-UV-absorbers and non-photoirritants) have been screened in an in vitro photoirritation assay using cultured cells [3T3 neutral red uptake (NRU) assay]. Treated cells were exposed to UVA (5 J/cm(2) in 50 min) and visible light in Earle's balanced salt solution and compared with dark controls. The 3T3 NRU assay has shown some promising results for screening photoirritants; however, it is likely that a battery of in vitro assays will be required.