<unk>  is an immunoglobulin E-mediated hypersensitivity that can be introduced through primary or secondary factors, or induced by exogenous photosensitization. Primary<unk>  is believed to be a type I hypersensitivity (a mild to severe reaction to an antigen including anaphylaxis) in which an antigen, or<unk> bstance provoking an immune response, is "induced by UV or visible radiation." Secondary<unk>  can occur when a person comes into contact with chemicals<unk> ch as tar, pitch, and dyes. People who use drugs<unk> ch as benoxaprofen or patients with erythropoietic protoporphyria may also contract this secondary form. These items that cause this photosensitivity are exogenous photosensitizers because they are outside of the body and cause it to have a greater sensitivity to light. Also, there have been a few unorthodox (unusual) causes of<unk> . For those<unk> sceptible to visible light, white T-shirts may increase the chances of experiencing an outbreak. In one case, doctors found that the white T-shirt absorbed UVA radiation from the<unk> n and transformed it into visible light which caused the reaction. Another patient was being treated with the antibiotic tetracycline for a separate dermatological disorder and broke out in hives when exposed to the<unk> n, the first case to implicate tetracycline as a<unk>  inducing agent. It is not yet known what specific agent in the body brings about the allergic reaction to the radiation. When patients with<unk>  were injected with an irradiated autologous serum, many developed urticaria within the area of injection. When people who did not have<unk>  were injected, they did not demonstrate similar symptoms. This indicates that the reaction is only a characteristic of the patients with<unk>  and that it is not phototoxic. It is possible that this photoallergen is located on the binding sites of IgE that are found on the<unk> rface of mast cells. The photoallergen is believed to begin its configuration through the absorption of radiation by a chromophore. The molecule, because of the radiation, is transformed resulting in the formation of a new photoallergen.
Solar urticaria
Cold urticaria
Heat urticaria
Aquagenic urticaria
Pressure urticaria
Cholinergic urticaria
Delayed pressure urticaria
Physical urticaria