The wavelength range of type III and IV spans from 400 to 500 nm, while type V can be caused by UVB radiation to visible light (280–600 nm). Type VI has only been known to occur at 400 nm.Another classification distinguishes two types. The first is a hypersensitivity caused by a reaction to photoallergens located only in people with SU; while the second is caused by photoallergens that can be found in both people with SU and people without it.A subgroup of solar urticaria, fixed solar urticaria, has also been identified. It is a rare, less intense form of the disease with wheals (swollen areas of the skin) that affect certain, fixed areas of the body. Fixed solar urticaria is induced by a broad spectrum of radiative energy with wavelengths ranging from 300 to 700 nm. Differential diagnosis
Polymorphous light eruption (PMLE) is the easiest disease to mistake for solar urticaria because the locations of the lesions are similar (the V of the neck and the arms). However, patients with SU are more likely to develop lesions on the face. Also, a reaction with PMLE will take a greater amount of time to appear than with solar urticaria. Lupus erythematosus has been mistaken for SU; however, lesions from lupus erythematosus will take a longer amount of time to go away. Furthermore, when being tested for the two diseases, patients with SU have a reaction immediately while patients with lupus erythematosus will have a delayed reaction.
Desensitization
This form of treatment is meant to reduce the intensity or altogether eliminate the allergic reactions people have by gradually increasing exposure to the form of radiation that brings about the reaction. In the case of solar urticaria, phototherapy and photochemotherapy are the two major desensitization treatments.Phototherapy can be used for prevention. Exposure to a certain form of light or UV radiation  enables the patient to build up a tolerance and outbreaks can be reduced. This type of treatment is generally conducted in the spring. However, the benefits of this  therapy only last for two to three days.Photochemotherapy, or PUVA, is considered superior to phototherapy because it produces a longer-lasting tolerance of the radiation that initiates the outbreak. When treatment first begins, the main goal is to build up the patients tolerance to UVA radiation enough so that they can be outdoors without having an episode of solar urticaria. Therefore, treatments are regulated at three per week while constantly increasing the exposure to UVA radiation. Once the patient has reached an adequate level of desensitization, treatments are reduced to once or twice per week. Immunoglobulin E (IgE) Therapy
Some patients and researchers have successfully treated solar urticaria with Omalizumab (trade name Xolair) which is commonly used to treat Idiopathic Urticaria. Omalizumab is a recombinant humanized monoclonal antibody against IgE.