[6] The disease itself can be difficult to diagnose properly because it is so similar to other dermatological disorders, such as polymorphous light eruption or PLE.

[8] The initial discovery of the disease is credited to P. Merklen in 1904, but it did not have a name until the suggestion of "solar urticaria" was given by William Waddell Duke in 1923.

People with extreme cases will also have reactions to artificial light sources that emit a UV wavelength.

Patients are subject to constant itching and pain, as within minutes of the initial exposure to UV radiation a rash will appear.

The urticarial reaction begins in the form of pruritus, later progressing to erythema and edema in the exposed areas of the skin.

If vast areas of the body are affected, the loss of fluid into the skin could lead to light-headedness, headache, nausea, and vomiting.

Also, if a large area of the body is suddenly exposed the person may be subject to an anaphylactic reaction.

[14] Solar urticaria is an immunoglobulin E-mediated hypersensitivity that can be introduced through primary or secondary factors, or induced by exogenous photosensitization.

In one case, doctors found that the white T-shirt absorbed UVA radiation from the sun and transformed it into visible light which caused the reaction.

[6] It is possible that this photoallergen is located on the binding sites of IgE that are found on the surface of mast cells.

When testing for its less intense form (fixed solar urticaria), phototesting should be conducted only in the areas where the hives have appeared to avoid the possibility of getting false-negative results.

The amount of radiation that the patient is exposed to is equal to that "received in an hour of midday summer sun."

[24][25] SU may be classified based on the wavelength of the radiative energy that causes the allergic reaction; known as Harber's classification, six types have been identified in this system.

[11] Type I solar urticaria is caused by UVB (ultraviolet B) radiation, with wavelengths ranging from 290 to 320 nm.

Fixed solar urticaria is induced by a broad spectrum of radiative energy with wavelengths ranging from 300 to 700 nm.

[23][26] 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).

Patients who have experienced solar urticarial symptoms from a young age could mistakenly be thought to have erythropoietic protoporphyria.

When the UV radiation or light comes in contact with a person with solar urticaria, histamine is released from mast cells.

Patients prescribed 50 milligrams four times per day have been able to sustain normal exposure to the sun without developing a reaction.

Exposure to a certain form of light or UV radiation enables the patient to build up a tolerance and outbreaks can be reduced.

[21] 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 patient's tolerance to UVA radiation enough so that they can be outdoors without having an episode of solar urticaria.

[8] When the treatment is a success, the patient's photosensitivity is decreased to the degree that they can undergo PUVA which can result in the relief of the urticarial outbreaks for an extended period of time.