The diagnosis of sun and heat allergies begins with a physician consultation. The physician will develop a detailed medical history. The physician may ask questions about any family history of allergies and asthma, and inquire about exposure to possible irritants, current medications, over-the-counter drugs, topical agents or any herbal products. It is important to discuss the use of all current medications or herbal remedies even if they are not used daily. The physician will examine the skin and ask questions about when the skin reaction occurs in relation to sun and heat exposure.

The physician may want to perform more detailed tests including:

• Skin biopsy. Laboratory test that examines a small piece of skin that has been removed by the physician.
  
  
• Blood tests. Tests that determine the amount of a given substance in the blood and identify abnormally high or low levels. Blood tests can identify any underlying diseases or conditions that may be causing the skin reaction.
  
  
• Phototesting. Test that exposes a small area of skin to measured amounts of ultraviolet light (an invisible form of radiation emitted by the sun, as well as sun lamps and tanning beds). If skin symptoms appear, the test will confirm that symptoms are related to sun exposure. Symptoms will usually appear within 30 minutes of exposure.
  
  
• Allergy tests. Tests that help to identify specific allergens. They may be skin tests, where the skin is pricked or injected with an allergen. If a red and swollen area of the skin appears at the test site, the test is positive for that allergen. Blood tests (e.g., RAST test) may be used to measure the levels of IgE in response to the introduction of a specific allergen.
  

  

Avoidance is the best treatment and prevention method for rashes or hives induced by exposure to sunlight or heat. For people who are sun-sensitive, sun protection is necessary regardless of weather conditions, and even in the shade. Covering the skin with clothing while exposed to sunlight will help to avoid the development of hives. Sunscreen or sunblock should be applied thoroughly on all areas of the skin that could be exposed to the sun (unless the sunscreen is an allergen capable of causing a photoallergic eruption).

Since sunscreen does not completely block the sun's rays, patients using sunscreen may still develop a reaction when exposed to the sun. Therefore, sunscreen should be used in conjunction with the avoidance of sunlight and not as a substitute for it.

Heat exposure can be avoided by covering the head and wearing cool, loose-fitting clothing when exposed to heat. Avoidance of hot baths or showers or other conditions involving warm temperatures is necessary. For people who have severe reactions and live in extremely hot climates, relocation may be beneficial.

Photoallergic eruptions can be treated by avoiding the sun while taking any medications that aggravate the condition. If other types of medications are available, discussion with a physician may identify alternate treatments that may not cause a photoallergic reaction.

A tepid shower or oatmeal bath may temporarily relieve the itchiness and irritation associated with mild hives. Cool compresses may also help with this type of discomfort.

Medications may be recommended or prescribed to treat moderate hives. The standard medications are antihistamines, which are available in both prescription and non–prescription forms. For more severe cases, corticosteroids may be recommended for the rapid reduction of swelling and itching. In extreme cases of solar urticaria, antimalarial drugs may be prescribed for their anti–inflammatory properties. Extreme cases of actinic prurigo may require a prescription of thalidomide for its immune system suppression properties.

Desensitization to sunlight or heat for PMLE, solar and heat urticaria are possible treatments for severe cases. Desensitization involves limited and controlled exposure to the allergen in a medical setting. A short dose of ultraviolet light is used to desensitize patients with PMLE and solar urticaria. Treatment of PMLE with a six week course of desensitization often provides a patient with protection for the entire summer. Limited and controlled exposure to heat may be used for heat urticaria.

Severe hives that create the potentially life-threatening allergic reaction known as anaphylactic shock should be treated under emergency medical care. Epinephrine injections (allergy kit) are required to reduce swelling and rapidly open breathing passages.