Cutaneous eruptions more or less confined to light-exposed areas are not uncommon. Despite numerous exhaustive reviews1-7 published in recent years, it is difficult for most practitioners to acquire a real diagnostic expertise in this field. Too often, the only characteristic feature in any given case is the distribution of the lesions. Hopefully, the following schemes will provide some new perspectives and helpful insights by plotting differentiating features as attributes against the primary light-sensitive dermatoses; by commenting on the more important (or more interesting) photosensitizing drugs and contactants; and, finally, by indicating which laboratory tests are likely to be of specific diagnostic value when the history and physical findings are inconclusive (as, for example, in protoporphyria).
I. The physical examination and history
B. Extrinsic photosensitivity
1. Internal agents* (drug-induced)
Sulfonamides†—uncommon with modern analogues, in contrast to the older drug, sulfanilamide
Thiazides,† quinethazone†—may have only pruritus in sun-exposed sites