Drug and chemical photosensitivity.

Chemical (especially drug-induced) cutaneous photo-sensitization is an increasing problem in dermatology. Various molecular, biochemical, and pathophysiologic processes are involved in translation of ultraviolet (UV) or visible radiation energy into phototoxic and/or photoallergic reactions in the skin. Phototoxicity presents in four major reaction patterns, depending on the target for photosensitization. Photoallergy is now confirmed as an immune system cell mediated photosensitization. Drug-induced photosensitivity is not necessarily a good reason for stopping therapy. Sunlight avoidance, appropriate protection with clothing, sunscreens, and drug dose reduction may allow continuation of treatment. However, future drug registration procedures may require more detailed testing both in vitro and in vivo, and good clinical trials for which suitable protocols are becoming available.