Photosensitization by coumarin derivatives.

Coumarin and several of its derivatives were investigated for their photosensitizing properties. With a few exceptions, the coumarins are potentially strong photocontact sensitizers but do not evoke phototoxic reactions. Substitution at the 6 or 7 positions of the benzopyrone ring confers photoallergenic capability, whereas hydrogenation abolishes activity. Photo-cross-reactions among closely related derivatives can develop. The action spectrum for contact photodermatitis extends from 360 nm down to at least 300 nm. Data are presented to show that the photocontact allergic response is related to the ultraviolet A dose and to the concentration of the offending chemical.