Sun allergy (photosensitivity)

What is a sun allergy?

Despite the name, a "sun allergy" is not truly an allergy to the sun. Instead, it is an immune system reaction in the skin triggered by sunlight, most often causing an itchy red rash. The medical term for this condition is Polymorphous Light Eruption (PMLE). The most common locations include the "V" of the neck, the back of the hands, the outside surface of the arms and the lower legs. In rare cases, the skin reaction may be more severe, producing hives or small blisters that may even spread to skin in clothed areas.

Sun allergies are triggered by changes that occur in sun-exposed skin. It is not clear why the body develops this reaction. However, the immune system recognizes some components of the sun-altered skin as "foreign," and the body activates its immune defenses against them. This produces an allergic reaction that takes the form of a rash, tiny blisters or, rarely, some other type of skin eruption.

Sun allergies occur only in certain sensitive people, and in some cases, they can be triggered by only a few brief moments of sun exposure. Some forms of sun allergy are inherited.

A few of the most common types of sun allergy are:

• Actinic prurigo (hereditary PMLE) — This inherited form of PMLE occurs in people of American Indian background, including the American Indian populations of North, South and Central America. Its symptoms are usually more intense than those of classic PMLE, and they often begin earlier, during childhood or adolescence. Several generations of the same family may have a history of the problem.
• Photoallergic eruption — In this form of sun allergy, a skin reaction is triggered by the effect of sunlight on a chemical that has been applied to the skin (often an ingredient in sunscreen, fragrances, cosmetics or antibiotic ointments) or ingested in a drug (often a prescription medicine). Common prescription medicines that can cause a photoallergic eruption include antibiotics (especially tetracyclines, fluoroquinolones and sulfonamides), NSAID pain relievers ibuprofen (Advil, Motrin and others) and naproxen sodium (Aleve, Naprosyn and others), and diuretics for high blood pressure and heart failure.
• Solar urticaria — This form of sun allergy produces hives (large, itchy, red bumps) on sun-exposed skin. It is a rare condition that most often affects young women.

Symptoms of sun allergy

Symptoms vary, depending on the specific type of sun allergy:

• PMLE — PMLE typically produces an itchy or burning rash within the first two hours after sun exposure. The rash usually appears on sun-exposed portions of the neck, upper chest, arms and lower legs. In addition, there may be one to two hours of chills, headache, nausea and malaise (a general sick feeling). In rare cases, PMLE may erupt as red plaques (flat, raised areas), small fluid-filled blisters or tiny areas of bleeding under the skin.
• Actinic prurigo (hereditary PMLE) — Symptoms are similar to those of PMLE, but they usually are concentrated on the face, especially around the lips.
• Photoallergic eruption — This usually causes either an itchy red rash or tiny blisters. In some cases, the skin eruption also spreads to skin that was covered by clothing. Because photoallergic eruption is a form of delayed hypersensitivity reaction, skin symptoms may not begin until one to two days after sun exposure.
• Solar urticaria — Hives usually appear on uncovered skin within minutes of exposure to sunlight.

Diagnosing sun allergy

If you have mild symptoms of PMLE, you may be able to diagnose the problem yourself by asking yourself the following questions:

• Do I have an itchy rash that occurs only on sun-exposed skin?
• Does my rash always begin within two hours of sun exposure?
• Do my symptoms first appear during the early spring, and then gradually become less severe (or disappear) within the following few days or weeks?

If you can answer "yes" to all of these questions, then you may have mild PMLE.

If you have more severe sun-related symptoms — especially hives, blisters or small areas of bleeding under the skin — your doctor will need to make the diagnosis. In most cases, your doctor can confirm that you have PMLE or actinic prurigo based on your symptoms, your medical history, family history (especially American Indian ancestry) and a simple examination of your skin. Sometimes, additional tests may be necessary, including:

• a skin biopsy, in which a small piece of skin is removed and examined in a laboratory
• blood tests to rule out other conditions, such as systemic lupus erythematosus (SLE or lupus) or discoid systemic lupus erythematosus
• photo-testing, in which a small area of your skin is exposed to measured amounts of ultraviolet light — If your skin symptoms appear after this exposure, the test confirms that your skin eruption is sun-related.

If you have symptoms of a photoallergic eruption, the diagnosis may take some detective work. Your doctor will begin by reviewing your current medicines as well as any skin lotions, sunscreens or colognes you use. The doctor may suggest that you temporarily switch to an alternate medication or eliminate certain skin care products to see whether this makes your skin symptoms subside. If necessary, your doctor will refer you to a dermatologist, a doctor who specializes in skin disorders. The dermatologist may do photopatch testing, a diagnostic procedure that exposes a small area of your skin to a combination of both ultraviolet light and a small amount of test chemical, usually a medicine or ingredient in a skin care product.

If you have symptoms of solar urticaria, your doctor may confirm the diagnosis by using photo-testing to reproduce your hives.

Expected duration of sun allergy

How long the reaction lasts depends on the type of sun allergy:

• PMLE — The rash of PMLE usually disappears within two to three days if you avoid further sun exposure. Over the course of the spring and summer, repeated sun exposure can produce hardening, a natural decrease in the skin's sensitivity to sunlight. In some individuals, hardening develops after only a few days of sun exposure, but in others it takes several weeks.
• Actinic prurigo (hereditary PMLE) — In temperate climates, actinic prurigo follows a seasonal pattern that is similar to classic PMLE. However, in tropical climates, symptoms may persist all year round.
• Photoallergic eruption — The duration is unpredictable. However, in most cases, skin symptoms disappear after the offending chemical is identified and no longer used.
• Solar urticaria — Individual hives typically fade within 30 minutes to two hours. However, they usually come back when skin is exposed to sun again.

Preventing sun allergy

To help prevent symptoms of a sun allergy, you must protect your skin from exposure to sunlight. Try the following suggestions:

• Before you go outdoors apply a sunscreen that has a sun protection factor (SPF) of at least 30 or above, with a broad spectrum of protection against both ultraviolet A and ultraviolet B rays.
• Use a sunblock on your lips. Choose a product that has been formulated especially for the lips, with an SPF of 30 or more.
• Limit your time outdoors when the sun is at its peak — in most parts of the continental United States, from about 10 a.m. to 3 p.m.
• Wear sunglasses with ultraviolet light protection.
• Wear long pants, a shirt with long sleeves, and a hat with a wide brim.
• Be aware of skin care products and medicines, especially certain antibiotics, that may trigger a photoallergic eruption. If you are taking a prescription medication, and you normally spend a great deal of time outdoors, ask your doctor whether you should take any special precautions to avoid sun exposure while you are on the drug.

Treating sun allergy

If you have a sun allergy, your treatment must always begin with the strategies described in the Prevention section. These will reduce your sun exposure and prevent your symptoms from worsening. Other treatments depend on the specific type of sun allergy:

• PMLE — For mild symptoms, either apply cool compresses (such as a cool, damp washcloth) to the areas of itchy rash, or mist your skin with sprays of cool water. You can also try a nonprescription oral (by mouth) antihistamine — such as diphenhydramine or chlorpheniramine (both sold under several brand names) — to relieve itching, or a cream containing cortisone. For more severe symptoms, your doctor may suggest a prescription-strength oral antihistamine or corticosteroid cream. If these remedies are not effective, your doctor may prescribe phototherapy, a treatment that produces hardening by gradually exposing your skin to increasing doses of ultraviolet light in your doctor's office. In many cases, five ultraviolet light exposures are given per week over a three-week period. If standard phototherapy fails, your doctor may try a combination of psoralen and ultraviolet light called PUVA; hydroxychloroquine; or beta-carotene supplements.
• Actinic prurigo (hereditary PMLE) — Treatment options include prescription-strength topical corticosteroids, phototherapy with special ultraviolet rays, and potentially thalidomide for severe cases.
• Photoallergic eruption — The first goal of treatment is to identify and eliminate the medicine or skin care product that is triggering the allergic reaction. Skin symptoms usually can be treated with a corticosteroid cream.
• Solar urticaria — For mild hives, you can try a nonprescription oral antihistamine to relieve itching, or an anti-itch skin cream containing cortisone. For more severe hives, your doctor may suggest a prescription-strength antihistamine, a topical or oral corticosteroid preparation, and/or phototherapy. For severe cases, omalizumab (Xolair) may be prescribed.

When to call a professional

Call your primary care doctor or a dermatologist if you have:

• an itchy rash that does not respond to over-the-counter treatments
• a rash that involves large areas of your body, including parts that are covered by clothing
• a persistent rash that covers sun-exposed areas of your face, especially if you are a woman or a person of American Indian heritage
• abnormal bleeding under the skin in sun-exposed areas.

Call for emergency help immediately if you suddenly develop hives together with swelling around your eyes or lips, faintness or difficulty breathing or swallowing. These may be signs of a life-threatening allergic reaction.

Prognosis

If you have a sun allergy, the outlook is usually very good, especially if you consistently use sunscreens and protective clothing. Most people with PMLE or actinic prurigo improve significantly within five to seven years after diagnosis, and almost everyone with photoallergic eruption can be cured by avoiding the specific chemical that triggers the sun allergy.

Of all forms of sun allergy, solar urticaria is the one that is most likely to be a long-term problem. However, in some people the condition eventually subsides.

Additional info

National Institute of Arthritis and Musculoskeletal and Skin Diseases
http://www.niams.nih.gov/

American Academy of Dermatology
http://www.aad.org/