Sun allergy is a broad term. It describes several conditions that cause an itchy rash to form on the skin after being in sunlight or other sources of ultraviolet (UV) radiation. Polymorphous light eruption is the most common form of sun allergy.

Some people have a hereditary type of sun allergy. Others develop symptoms only when triggered by another factor — such as taking medication or touching certain plants. Other types of sun-related reactions occur for reasons that are unclear.

Mild sun allergy may clear up without treatment. Severe rashes may be treated with steroid creams or pills. If you have severe sun allergy, you may need to take preventive steps. For example, wear clothing that shields you from the sun.

Causes of sun allergy include immune system reactions to sunlight, certain medications and chemicals that 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:

• Contact with certain substances. Some sun 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 chemicals used in some 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 a blood relative 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 sun exposure between 10 a.m. and 4 p.m. The sun's rays are strongest during these hours. Try to schedule outdoor activities for other times. If you can't do that, limit the time you're in the sun. Seek shade when possible.
• Avoid sudden exposure to lots of sunlight. Many people have sun allergy symptoms seasonally. Symptoms occur when daylight hours get longer and people are exposed to more sunlight. At these times, gradually increase the amount of time you spend outdoors so that your skin has time to adapt to increased 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.

• Apply sunscreen. Use a water-resistant, broad-spectrum sunscreen with an SPF of at least 30, even on cloudy days. Apply sunscreen generously, and reapply every two hours — or more often if you're swimming or perspiring.

  If you're using a product that contains physical blockers (titanium dioxide, zinc oxide), apply it over any other products you're wearing — except insect repellent. Insect repellent goes on last. Physical blockers provide the most effective protection for sensitive skin.

  The Food and Drug Administration (FDA) requires all sunscreen to retain its original strength for at least three years. Check sunscreen labels for directions on storing and expiration dates. Throw away sunscreen if it's expired or more than 3 years old.

• 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.
• Apply UV-blocking window film. Put a UV-blocking film on the windows of your home and car.

Your health care provider may diagnose sun allergy by looking at your skin. You might need tests, such as:

• Ultraviolet (UV) light testing. Also called phototesting, this exam is used to see how your skin reacts to light from a special lamp. This can help pinpoint which type of 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 to your skin, typically on the back. A day later, one of the areas receives a measured dose of UV 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. Your health care provider may have you undergo these tests if your symptoms might be caused by an underlying condition, such as lupus. With these tests, a blood sample or a skin sample (biopsy) is taken for examination in a laboratory.

Treatment for sun allergy depends on the type you have and your symptoms. For mild symptoms, you may need to simply avoid the sun for a few days.

Medications

Creams containing corticosteroids are available in both nonprescription and prescription strengths. For a severe reaction, your health care provider may have you take prescription corticosteroid pills, such as prednisone, for a short time.

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

Phototherapy

If you have a severe sun allergy, your health care provider may suggest gradually getting your skin used to sunlight each year as the daylight hours get longer. In phototherapy, a special lamp is used to shine ultraviolet light on areas of the 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 health care provider about whether you can stop taking them if they are making your skin more sensitive to the sun.
• Apply moisturizers. Moisturizing skin lotions can help relieve irritation caused by dry, scaly skin.

You're likely to start by seeing your 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), you might need 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 health care provider 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?