dermatologic disorders
Photosensitivity
Solar urticaria
In certain patients, urticaria develops at a site of sun exposure within a few minutes. Lesions generally resolve within 24 hours. Rarely, if large areas are involved, syncope, dizziness, wheezing, and other systemic symptoms may develop. Etiology is unclear but may involve endogenous skin constituents functioning as photoallergens, leading to mast cell degranulation as in other types of urticaria. Solar urticaria can be distinguished from other types of urticaria in that wheals in solar urticaria occur only on exposed skin after ultraviolet (UV) light exposure. Solar urticaria can be classified based on the component of the UV spectrum (UVA, UVB, and visible light) that causes lesions. If necessary, patients can be tested by exposing part of the skin to natural light or artificial light at particular wavelengths (phototesting). Treatment of solar urticaria can be difficult and may include H1 blockers, topical corticosteroids, and sunscreens. If standard treatment fails, desensitization with narrow-band UVB or PUVA (psoralen plus ultraviolet A), may be tried.Omalizumab(anti-IgE therapy) has been successful in a small number of patients. The disorder is chronic and can wax and wane over years. 