Identification of topical photosensitizing agents in humans

A method is described for the detection of topical photosensitizers in humans. Test agents were applied to the untanned midback under an occlusive dressing for 6 hr and then exposed to broad-spectrum radiation containing UV-A and visible wavelengths from a Xenon arc source. Well-known topical photosensitizers were readily identified. It was found that with certain poorly-penetrating substances, such as water-soluble dyes, applications to scarified skin were necessary to reveal phototoxic activity. In addition, these dyes were activated by wavelengths in the visible region of the spectrum.