What is solar urticaria?

Urticaria, or hives, may be triggered by ultraviolet or even visible light. The urticarial papules or plaques usually develop on exposed areas within minutes of sun exposure and are accompanied by pain or pruritus. Rarely, systemic reactions leading to anaphylactic shock can occur. Solar urticaria is a photoallergic reaction (type I hypersensitivity response) and is most likely IgE mediated, though direct degranulation of mast cells may also be a pathogenic mechanism.

Ryckaert S, Roelandts R: Solar urticaria: a report of 25 cases and difficulties in phototesting, Arch Dermatol 134:71–74, 1998.