With summer comes increased exposure to an often lesser known physical urticaria trigger : the sun !
Solar urticaria (SU) is a rare type of physical urticaria that is triggered by exposure to UV radiation, mostly often from the sun, but can also occur following exposure to artificial lighting. It represents about 4% of patients with photosensitive disorders. It is different from from the more common Polymorphous Light Eruption (PMLE) in that symptoms appear minutes to an hour after exposure and goes away quickly, while the PMLE rash appears later and lasts longer. In addition to the rash, people with solar urticaria may experience nausea, light-headedness, bronchospasm, a headache or even an anaphylactic reaction. The reaction is often specific to a narrow band of wavelengths. Type I SU is caused by UVB (290-320nm), Type II SU by UVAs (320-400nm). Some types can present sensitivity to visible light. It is distinct from heat rash (cholinergic urticaria), because the rash will develop even in the absence of heat (ex.: on the hands and face in the winter). The cause are not well known
Treatment for solar urticaria includes antihistamines (the preferred ones being fexofenadine and diphenhydramine), omalizumab (Xolair), immunosuppression (prednisone and cyclosporin) and, in extreme cases, plasmapheresis - extracting the plasma from the blood to return the red blood cells to the body, which is thought to remove the factor in the blood that causes SU.
Life with SU can be challenging, as complete avoidance of UV light is difficult, especially in the summer. Patients are advised to wear clothing that covers their skin and high SPF sunblock and to avoid direct sunlight as much as possible.