Solar urticaria.

Solar urticaria is a rare disorder in which patients develop urticarial lesions after exposure to light from the sun or other sources. The etiology is unknown: some cases appear to be mediated by IgE, but other mechanisms may ultimately be found to be more significant. This disease typically persists for years, but may resolve spontaneously. Although fatalities have not yet been reported, episodes of solar urticaria have produced near-fatal accidents. At best, treatment is difficult, but some techniques have afforded some patients substantial or total relief, even if only temporarily.