Generation of reactive intermediates in photoallergic dermatitis

Photosensitivity disorders are cutaneous reactions caused or amplified in their severity by sunlight, normally ultraviolet radiation (UVA or UVB). These reactions appear when xenobiotics are topically or systemically administered, and the individuals are exposed to solar or artificial light.

Photoallergic reactions seem to be initiated by covalent binding of the photosensitizer to a skin protein, forming adducts capable of interacting with the immune system. The most frequent reactions of this type (photoallergic dermatitis) are induced by drugs and mediated by T cells. Diagnosis of photoallergy requires identification of the responsible agent, which is not always clear-cut. Photopatch testing is the method of choice for definitive diagnosis.

In the current review, some specific examples of photoallergic xenobiotics are given. They include nonsteroidal anti-inflammatory drugs, antibiotics, platelet aggregation inhibitors, and sunscreens. In general, they are taken from the scientific literature published during the last decade, with particular emphasis on the most recent articles. The focus is on the mechanistic aspects, specifically on the generation of reactive intermediates capable of reacting with proteins.