Sun allergy

[David Baxter PhD]

Sun allergy
Mayo Clinic
April 29, 2010

Sun allergy is a condition in which sunlight triggers a skin reaction. For most people, sun allergy symptoms include an itchy red rash in areas that have been exposed to sunlight. A severe sun allergy may cause hives, blisters or other symptoms. There are several types of sun allergy — including polymorphic light eruption (PMLE), actinic prurigo, chronic actinic dermatitis (CAD) and solar urticaria.

Symptoms
Sun allergy symptoms depend on the particular type of sun allergy you have.

• Polymorphic light eruption (PMLE) symptoms usually start within minutes to several hours after exposure to sunlight. A reaction usually starts with itchy skin and tiny bumps (papules) that appear whitish or yellowish on a red background. Flat bumps (plaques) may develop. Inflamed blood vessels can cause your skin to become red and swollen. PMLE, sometimes called sun poisoning, may affect the neckline, the backs of the arms, the face and the hands. Symptoms usually go away within a few days when the affected areas are protected from sunlight. For most people, PMLE occurs in the spring and early summer. It's the most common type of sun allergy.
• Actinic prurigo usually occurs in children and young adults. Symptoms can include red, raised patches of skin and itchy bumps that may extend onto skin that wasn't exposed to sunlight. Fluid filled bumps may form and crack open. Actinic prurigo often causes chapped and split lips (cheilitis), and can affect the cheeks, neck, ears, arms and hands. In some people, actinic prurigo leaves scars. Symptoms generally start in the summer months and improve by late autumn.
• Chronic actinic dermatitis can cause thick patches of dry, itchy and inflamed skin on the face, scalp, back and sides of the neck, upper chest, and backs of the arms and hands. Large affected areas may have "islands" of exposed skin that aren't affected. In some cases, symptoms occur on the palms of the hands and bottoms of the feet. Symptoms of chronic actinic dermatitis are similar to symptoms caused by direct contact with an allergy-causing substance (contact dermatitis).
• Solar urticaria symptoms start within minutes of exposure to sunlight and can include hives, itching and blisters. Solar urticaria can affect both exposed areas and areas covered by clothes. It occurs most often in older adults. Symptoms usually improve within an hour after covering exposed skin.

When to see a doctor
See a doctor if you have unusual, bothersome skin reactions after exposure to sunlight. For severe or persistent symptoms, you may need to see a doctor who specializes in diagnosing and treating skin disorders (dermatologist).

Causes
Allergic reactions to sunlight occur when ultraviolet radiation triggers changes in your skin cells. These changes cause your immune system to mistakenly identify proteins in your skin cells as harmful invaders. Your immune system then releases antibodies that attack the cells, and this leads to symptoms.

For most people with a sun allergy, exposing bare skin to bright sunlight during the spring or summer triggers the allergic skin reaction. However, some people can have a reaction during winter months. In people who have a severe sun allergy, an allergic reaction may even be triggered by indoor lights.

Certain medications, chemicals and medical conditions can make the skin more sensitive to the sun (photosensitivity). For example, an ingredient in your shampoo or having a condition such as lupus can increase photosensitivity. In most cases this isn't a true allergic reaction. However, it can cause symptoms similar to those caused by a sun allergy — and if you already have a sun allergy, it can make your symptoms worse.

It isn't clear why some people have a sun allergy, and others don't. Inherited traits may play a role.

Risk factors
Risk factors for having an allergic reaction to sunlight depend on your particular condition. These include:

• Race. Anyone can have a sun allergy, but certain sun allergies are most common in people of certain racial backgrounds. For example, the most common type of sun allergy (polymorphic light eruption) occurs mostly in Caucasians. Actinic prurigo is most common in Native Americans.
• Sex and age. Polymorphic light eruption (PMLE) is most common in girls and in women under age 30. However, a certain type of PMLE known as juvenile spring eruption occurs in boys and young men. Chronic actinic dermatitis most often affects older men who've spent a lot of time in the sun.
• Exposure to certain substances. Some skin allergy symptoms are triggered when your skin is exposed to a certain substance and then to sunlight. Some common substances responsible for this type of reaction include fragrances, disinfectants and even certain sunscreens.
• Taking certain medications. A number of medications can make the skin more sensitive to sunlight — including tetracycline antibiotics, nonsteriodal anti-inflammatory medications (such as ketoprofen) and sulfa-based drugs. Reactions to oral medications are less common than reactions to medications you apply to your skin.
• Having another skin condition. Having atopic dermatitis or another type of dermatitis increases your risk of having a sun allergy.
• Having relatives with a sun allergy. You're more likely to have a sun allergy if you have a blood relative — such as a sibling or parent — with a sun allergy.

Complications Sun allergy symptoms usually go away when the affected areas are protected from sunlight. They generally don't cause any long-term complications. However, in some people, severe actinic prurigo leaves pitted scars.

Tests and diagnosis Your doctor will want to make sure your skin reaction isn't due to something other than a sun allergy. A number of conditions can cause similar symptoms. In some cases, a skin allergy can be diagnosed by answering questions or by having your doctor examine the affected areas when symptoms are present. However, if the diagnosis isn't clear-cut, you may need tests to help identify what's going on. If this is the case, you'll most likely need to see a dermatologist.

Tests to diagnose skin reactions caused by sun exposure can include:

• UV light testing. Also called phototesting, this exam is used to see how your skin reacts to different wavelengths of ultraviolet light from a special type of lamp. Determining which particular kind of UV light causes a reaction can help pinpoint which sun allergy you have.
• Photopatch testing. This type of test is used if your doctor suspects something you've come in contact with makes your skin react to sunlight. To do the test, your doctor will apply two identical patches of a substance that may be causing a reaction to your skin. After 24 hours, your doctor will expose one area to UV light, but not the other. If a reaction occurs only on the exposed area, it's likely your reaction is linked to the substance in question. Light testing and photopatch testing are generally available only at specialized clinics.
• Blood tests and skin samples. These tests usually aren't needed. However, your doctor may order one of these tests if he or she suspects your symptoms might be caused by an underlying condition such as lupus instead of a sun allergy. With these tests, a blood sample or a skin sample (biopsy) is taken for further examination in a laboratory.

Treatments and drugs
Treatment depends on the particular type of sun allergy you have. It may include:

• Corticosteroid creams. These creams are available over-the-counter and in stronger, prescription form. For example, hydrocortisone medications (Cortaid, others) are available over-the-counter and triamcinolone medications (Kenalog, others) require a prescription.
• Oral antihistamines. These medications block histamines, symptom-causing chemicals released during an allergic reaction. Your doctor may recommend you use over-the-counter antihistamine pills, or he or she may write you a prescription. Examples of over-the-counter antihistamines include loratadine (Claritin, Alavert) and cetirizine (Zyrtec). Older over-the-counter antihistamines such as diphenhydramine (Benadryl) and clemastine (Tavist) work as well as newer ones, but can make you drowsy. Prescription antihistamines include desloratadine (Clarinex), fexofenadine (Allegra), hydroxyzine (Vistaril) and levocetirizine (Xyzal).
• Oral corticosteroids. For a severe allergic skin reaction, you may benefit from a short course of these powerful anti-inflammatory medications. In some cases, an oral corticosteroid such as prednisone is given prior to a period of sunlight exposure, such as before a summer vacation. Oral corticosteroids can cause serious side effects when used long term, so they're used to prevent and relieve severe sun allergy symptoms only on a short-term basis.
• Other medications. In some cases, drugs usually used to treat other conditions are used to treat sun allergies. For example, the malaria medication hydroxychloroquine may ease symptoms of polymorphic light eruption and other sun allergies. In some cases, antibiotics — generally used to treat infections — are used for chronic actinic dermatitis.
• Ultraviolet light therapy. This treatment is also called phototherapy. A special lamp is used to shine ultraviolet light on areas of your body that are often exposed to the sun. It's generally done a few times a week over a period of several weeks each spring. During the course of treatments, your doctor will gradually increase the dose of UV radiation. Your skin becomes accustomed to UV light, reducing symptoms caused by sun exposure. This treatment is generally available only at specialized clinics.

Lifestyle and home remedies
These steps may help relieve sun allergy symptoms:

• Avoid sun exposure. Most sun allergy symptoms improve quickly when the affected areas are no longer exposed to sunlight.
• Apply skin moisturizers. Moisturizing skin lotions can help relieve irritation caused by dry, scaly skin.
• Use soothing skin remedies. Home remedies that may help include calamine lotion and aloe vera.

Prevention
If you have a sun allergy or an increased sensitivity to the sun, you can help prevent a reaction by taking these steps:

• Limit your time in the sun. Stay out of the sun between 10 a.m. and 3 p.m. when the sun is brightest.
• Avoid sudden exposure to lots of sunlight. Many people have sun allergy symptoms when they are exposed to more sunlight in the spring or summer. Gradually increase the amount of time you spend outdoors so that your skin cells have time to adapt to sunlight.
• Wear sunglasses and protective clothing. Long-sleeved shirts and wide-brimmed hats can help protect your skin from sun exposure. Avoid fabrics that are thin or have a loose weave — UV rays can pass through them. You may want to consider wearing clothes specifically designed to block UV rays, which can be found at sporting goods stores.
• Apply sunscreen frequently. Use broad-spectrum sunscreen with a sun protection factor (SPF) of 30 or higher on exposed skin. Reapply sunscreen every two hours.

References

1. Gambichler T, et al. Immunologically mediated photodermatoses diagnosis and treatment. American Journal of Clinical Dermatology. 2009;10:169.
2. Millard T, et al. Photosensitivity disorders cause, effect and management. American Journal of Clinical Dermatology. 2002;3:239.
3. Ofori AO, et al. Overview of cutaneous photosensitivity: Photobiology, patient evaluation, and photoprotection. UpToDate Inc. . Accessed March 23, 2010.
4. Ferguson J. Diagnosis and treatment of the common idiopathic photodermatoses. Australasian Journal of Dermatology. 2003;44:90.
5. Ofori AO, et al. Photosensitive disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment. UpToDate Inc. . Accessed March 23, 2010.
6. Lenane P, et al. Sunscreens and the photodermatoses. Journal of Dermatological Treatment. 2001;12:53.