Solar urticaria: case report and phototesting with lasers.

Solar urticaria (SU) is a rare photosensitivity disease characterized by itching, erythema, and whealing immediately after exposure to sunlight or artificial radiation. A 28-year-old female whose history was strongly suggestive of SU, but who failed to demonstrate any photosensitivity on standard light testing with a slide projector as well as UVA and UVB broadband bulbs, developed urtication when provoked with the argon-pumped dye laser at 610 nm, 650 nm, and 690 nm. Lasers may be useful tools in performing visible phototesting, especially at longer wavelengths, in patients with SU because they are powerful and efficient, whereas slide projectors have relatively little emission toward the red wavelengths and consequently may fail to evoke an urticarial response in patients, such as ours, with high-threshold, red light-induced SU.