Drug-induced photosensitivity.

Drug-induced photosensitivity is common. The principal mechanism of systemic drug photosensitivity is phototoxicity and the principal mechanism of topical drug photosensitivity is photoallergy. Photopatch testing is helpful to determine suspected topical agent photoallergies (eg, from ultraviolet filters in sunscreens) but generally not helpful in detecting systemic drug photosensitivity. Drug-induced photosensitivity is usually best managed by stopping the suspected drug. Other measures, including phototherapy using wavelengths that do not elicit the response, are sometimes necessary.