Solar Urticaria, also called sun allergy rash, is one of the types of physical urticaria in which exposure to the sun (or other ultraviolet radiation) causes a hypersensitive reaction in the skin (also sometimes referred to as a heat rash). This reaction may occur immediate upon exposure to the sun or solar radiation, or may occur hours later (delayed-onset solar urticaria). This reaction most commonly affects areas of the skin that are unprotected by clothing, although some individuals may experience the rash-like reaction even on parts of the body protected by clothing.
Solar urticaria is a relatively uncommon hives disorder, and tends to occur less than other physical urticaria forms, such as dermatographic urticaria or cholinergic urticaria. Like other physical urticaria disorders, this can be extremely difficult for sufferers to experience. The sun allergy rash that can be left on the skin can be itchy, painful, or simply embarrassing to the individual.
Solar urticaria often develops suddenly, without any prior history. It may also develop slowly over time, into a more serious case. Many physical urticaria conditions develop in the late teens and early 20’s, however, symptoms may develop at any age, including infants to the elderly. The condition may persist for years, and may disappear or go into remission by itself. In cases where a known cause is discovered, removal of the antigen or medication may allow symptoms to resolve.
Solar Urticaria Signs & Symptoms
When a person with solar allergies is exposed to the sun, symptoms usually develop rapidly. Solar urticaria symptoms include itching (pruritus), stinging or tingling of the skin, a burning sensation, and small pinpoint hives after direct exposure. In more serious cases (or after prolonged sun exposure), the hives may develop into a large rash of erythema and edema.
It is not uncommon for more severe symptoms do develop if the person has a severe case. In the most severe cases, solar urticaria can progress to more serious symptoms such as dizziness, stomach cramping, headaches, or even anaphylactic shock. Individuals at risk for developing anaphylactic shock should consult their physicians about a prescription epi-pen for emergencies.
Once the individual is no longer exposed to the sun or source of radiation, the symptoms will begin to resolve. The symptoms may disappear within minutes, or can last as long as a few hours. Rarely, a rash may persist for a few days.
Solar Urticaria Diagnosis
Solar urticaria is diagnosed in various ways. Many times, a physician may ask the patient to describe the rash, and present a picture of possible. In addition, the following tests are sometimes used: Photopatch test, photoprovocation testing, and skin biopsy after hives reaction. Physicians also regularly do other diagnostic tests, such as blood work, urine, or vitamin tests to rule out other health concerns.
- Photopatch Test— In this test, the suspecting sensitizer agent is applied to the skin for up to 24-48 hours, usually under a dressing. The sensitizer is usually a suspected allergen. The skin is then carefully monitored to see if the sensitizer elicits a reaction. After this period, if no reaction has occurred, doctors may apply UV radiation to the same area on the skin where the sensitizer was applied. If the skin reddens or forms a urticaria reaction on the area, the test is positive.
- Phototesting–Phototesting seeks to discern which dosages and types of UV radiation are responsible for the hypersensitive reaction. Coverings are applied to the skin, leaving only small slits of skin visible. Then, varying amounts of UVA and UVB radiation are applied to the different areas of the skin samples. The skin areas are then monitored for reactions. Since some individuals with solar urticaria may experience varying reactions based on the different types of solar radiation, this test can be useful in determining which wavelengths are most harmful and elicit the most severe responses.
- Photoprovocation Testing–Photoprovocation testing seeks to apply radiation to the skin resembling common radiation experienced outdoors. If the skin reacts, samples may be taken for inspection under a microscope.
Like many urticaria conditions, diagnosis and testing is not always exact, and it can be difficult for both the doctor and patient to be properly diagnosed. What complicates ths further is that individuals with a physical urticaria also have other overlapping allergic conditions, such as food allergies, asthma, etc.
Solar Urticaria Causes
Since there are different subsets and types of solar reactions, it can be difficult to identify the solar urticaria causes. For some individuals, solar urticaria is induced when a skin is exposed to sun, even without any chemicals applied to the skin. Some suggest that this radiation may cause subtle changes in the skin or mast cells, such as an antigen (photo-allergen) or new protein formation/binding when introduced to the radiation, which alerts the immune system to respond in a hypersensitive reaction.
Other urticaria causes can include chemical reactions with the skin’s surface, which are intensified or activated by sun exposure. This can include reactions or allergies to skin care products, dyes, detergents, and other chemicals.
Antibiotics and other medications can also cause hypersensitivity in the skin, although this often resolves once the medications are no longer taken.
Generally speaking, all urticaria reaction generally involve the mast cells releasing the chemical known as histamine. Histamine is released when mast cells “de-granulate” or break down. Histamine then leaks into the surrounding tissues, and causes the itching, stinging, and burning sensation.
Solar Urticaria Treatment or Cure
Treatments for solar urticaria depend on the cause and type. For individuals experiencing photo-sensitivity to medications or skin care products, it is recommended to simply avoid sun exposure or switch to alternative products. For individuals with hives caused by sun exposure who do not have a known cause, some of the treatments below can be beneficial:
- Antihistamines–Antihistamines can help lesson symptoms of redness, itching, stinging, and burning. Sometimes, stronger doses or combinations of different types are prescribed for difficult cases. Always consult a doctor before using any medications.
- Sun Protection–Covering the skin with clothing and large hats, and limiting sun exposure may be helpful in the short-term, especially for those who only experience a reaction on uncovered skin.
- Immunosuppressants–Drugs such as corticosteroids may be given for short term relief in the most severe cases. However, these drugs are not a long term solution, carry significant side effects, and may have a “rebound” effect. Therefore, these should be avoided if possible, and only used in very serious cases for a short term relief.
- Photo-therapy–For some individuals with physical hives or sun allergy symptoms, it may be helpful to administer small doses of UV radiation. This can be gradually increased until the body develops a tolerance to the UV light. This also carries potential side effects such as increased skin cancer risk and premature aging.
- Diet Modifications–Some individuals with physical urticaria may see benefits from diet modifications. Removing known allergens and performing allergy elimination diets (in addition to allergy testings), may help reduce inflammation and symptoms associated with allergic disorders and physical hives.