Sun allergy is a term often used to describe a number of conditions in which an itchy red rash occurs on skin that has been exposed to sunlight. The most common form of sun allergy is polymorphic light eruption, also known as sun poisoning.

Some people have a hereditary type of sun allergy. Others develop signs and symptoms only when triggered by another factor — such as a medication or skin exposure to plants such as wild parsnip or limes.

Mild cases of sun allergy may clear up without treatment. More-severe cases may be treated with steroid creams or pills. People who have a severe sun allergy may need to take preventive measures and wear sun-protective clothing.

The appearance of skin affected by sun allergy can vary widely, depending on what's causing the problem. Signs and symptoms may include:

• Redness
• Itching or pain
• Tiny bumps that may merge into raised patches
• Scaling, crusting or bleeding
• Blisters or hives

Signs and symptoms usually occur only on skin that has been exposed to the sun and typically develop within minutes to hours after sun exposure.

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).

Certain medications, chemicals and medical conditions can make the skin more sensitive to the sun. It isn't clear why some people have a sun allergy and others don't. Inherited traits may play a role.

Risk factors for having an allergic reaction to sunlight include:

• Race. Anyone can have a sun allergy, but certain sun allergies are more common in people with lighter skin.
• Exposure to certain substances. Some skin allergy symptoms are triggered when your skin is exposed to a substance and then to sunlight. Common substances responsible for this type of reaction include fragrances, disinfectants and even some chemicals used in sunscreens.
• Taking certain medications. A number of medications can make the skin sunburn more quickly — including tetracycline antibiotics, sulfa-based drugs and pain relievers, such as ketoprofen.
• Having another skin condition. Having dermatitis increases your risk of having a sun allergy.
• Having blood relatives with a sun allergy. You're more likely to have a sun allergy if you have a sibling or parent with a sun allergy.

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

• Avoid the sun during peak hours. Try to stay out of the sun between 10 a.m. and 4 p.m.
• 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.
• Use sunscreen. Use a broad-spectrum sunscreen with an SPF of at least 30. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring.
• Avoid known triggers. If you know that a certain substance causes your skin reaction, such as a medication or contact with wild parsnip or limes, avoid that trigger.

In many cases, doctors can diagnose sun allergy simply by looking at the skin. But if the diagnosis isn't clear-cut, you may need tests to help identify what's going on. These tests may include:

• Ultraviolet (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 test shows whether your sun allergy is caused by a sensitizing substance applied to your skin before you go into the sun. In the test, identical patches of common sun allergy triggers are applied directly to your skin, typically on your back. A day later, one of the areas receives a measured dose of ultraviolet rays from a sun lamp. If a reaction occurs only on the light-exposed area, it likely is linked to the substance being tested.
• 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.

Treatment depends on the type of sun allergy you have. For mild cases, simply avoiding the sun for a few days may be enough to resolve the signs and symptoms.

Medications

Creams containing corticosteroids are available over-the-counter and in stronger prescription forms. For a severe allergic skin reaction, your doctor may prescribe a short course of corticosteroid pills, such as prednisone.

The malaria medication hydroxychloroquine (Plaquenil) may ease the symptoms of some types of sun allergies.

Therapy

If you have a severe sun allergy, your doctor might suggest gradually getting your skin used to sunlight each spring. In 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 several weeks.

These steps may help relieve sun allergy symptoms:

• Avoid sun exposure. Most sun allergy symptoms improve in less than a day or two if you keep the affected skin out of the sun.
• Stop using medications that make you sensitive to light. If you're taking medications for other conditions, talk with your doctor about whether you can stop taking them if they are making your skin more sensitive to the sun.
• Apply skin moisturizers. Moisturizing skin lotions can help relieve irritation caused by dry, scaly skin.
• Use soothing skin remedies. Try applying calamine lotion or a lotion with aloe vera to ease your symptoms.

You're likely to start by seeing your family doctor or primary care provider. Or when you call to set up an appointment, you may be referred to a doctor who specializes in skin conditions (dermatologist).

At the time you make the appointment, be sure to ask if you need to do anything in advance. For example, if you're going to have tests that check for a reaction to ultraviolet light (phototesting), your doctor may ask you to stop taking certain medications beforehand.

What you can do

Before your appointment, you may want to list answers to the following questions:

• How long after exposure to the sun did your symptoms begin?
• What type of symptoms did you experience?
• Have your symptoms worsened or gotten better?
• Have you ever had these types of symptoms before?
• What medications and supplements do you take regularly?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Examples may include:

• What parts of your body are affected?
• Exactly what does the affected skin look like?
• How severe are your symptoms?
• How long does your skin reaction last?
• Do you have itching or pain?
• Does your skin react just to direct sunlight or also to sunlight shining through window glass?
• Does anyone else in your family have skin reactions to sunlight or other allergic skin conditions?
• What products do you use on your skin?