Fixed solar urticaria with delayed onset.

Fixed solar urticaria (FSU) is an extremely rare type of solar urticaria characterized by urticarial wheals appearing frequently confined to fixed areas of the skin. After a few minutes of exposure to sunlight or other sources of radiation, urticarial lesions can usually be induced exclusively in the same localization. We report a case of delayed onset FSU occurring 6 hours after exposure to ultraviolet A and B light.