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Allergic to the Sun? You're Not Alone
Sun allergies are a widespread phenomenon, affecting in varying degrees 10-15% percent of the population.
Carla Cantor, Medical Writer

Childhood summers on Cape Cod. Ah...the memories. Seafood, sunsets, ice-blue water, pristine beaches, majestic dunes, and Mom plopped under a beach umbrella. Ninety degrees, and there she'd be in her huge, floppy sun hat and long-sleeved, floor-length white robe. We used to call her the "white mummy."

It was hard for us to believe, but Mom was allergic to the sun. No one we knew had this problem--although it is in fact fairly common, especially among women in their 30s and 40s. The allergy surfaced the summer of my mother's 33rd birthday when one day she broke out in a patchwork of blotchy, red blisters. The first doctor she saw said it was poison ivy and had her bake in the sun. The rash got worse. Finally, a dermatologist diagnosed polymorphic light eruption, or PMLE, a rash that's caused by sun exposure in those who are photosensitive.

Be Careful in the Sun

"Sun allergies are a widespread phenomenon, affecting in varying degrees 10-15% percent of the population," says John Epstein, MD, clinical professor of dermatology at University of California School of Medicine (San Francisco). But PMLE is generally overlooked, according to Epstein, who specializes in photosensitivity disorders, "both by practitioners who don't recognize sun reactions, and by the public, who think they have something else, like poison ivy or an allergy to their sunscreen."

For most, PMLE is a mild annoyance. In them, it causes a burning sensation or itch that lasts a few days; but in a small percentage of people who are severely light sensitive, symptoms may be disabling. Though medications help, normal activities may be impossible. Frank DeLaus, MD, a dermatologist in Utica, New York, tells of one patient who couldn't even take out the garbage without worrying about a skin eruption. My mother, too, had a fairly tough case. Nevertheless, she rarely complained, wearing cover-ups and sunscreen while the rest of us tanned in sun and surf. The allergy, she told us, was probably saving her from both skin cancer and wrinkles. (And it's true that today the skin of her sun-baked friends does look more leathery than hers!)

Hormones and Heredity

What causes polymorphic light eruptions?

Scientists believe that in sun-sensitive individuals the sun's ultraviolet (UV) rays interact with a compound in the body that suppresses or alters the skin's immune function. That causes the inflammatory rash. The inflammation is fueled by UV-B rays (which can be blocked by most sunscreens) and by longer UV-A rays, which penetrate more deeply. UV-A rays are not blocked by window glass, which explains why allergic reactions can occur while riding in a car, and why sunscreens--most of which only partially block UV-A rays--may not be an effective defense. Tanning booths and indoor sunlamps, which transmit large amounts of UV-A radiation, can be even more problematic than natural sunlight.

Why sunlight triggers PMLE in some people and not others is not entirely understood, but scientists suspect that heredity and hormones both contribute. The condition generally occurs in women between the ages of 20 and 40, although it sometimes affects children. In men, PMLE is less common.

"There is no question that PMLE has a genetic component, " says UCSF's Epstein. "Sun sensitivity tends to run in families." Studies have shown that anywhere from 15 to 50% of sun allergies may be hereditary. Environment appears to play a role as well. Skin reactions tend to be most common in people from temperate climates where tropical sunlight is a rarity. According to the Dermatology Web site for Waikato Hospital in Hamilton, New Zealand (www.dermnet.org), as many as 10% of Northern European women holidaying in the Mediterranean each year come down with PMLE. Skin reactions are less common in people who are exposed to sunlight all year round.

Drugs/Disease Causal, Too

Certain medications and products can also cause your skin to be extra sensitive to sunlight, as can some diseases. So, if you get a rash or an unusually severe burn after being out in the sun only a short time, don't automatically assume that you have an allergy. Chemicals that produce an intense reaction after a brief exposure to the sun are called photosensitizers. You don't have to be sun sensitive to have a reaction to a photosensitizing drug or product, although not everyone will have a reaction. Oddly, you may have the reaction once and not again.

Some common photosensitizing drugs include acne medicines, antihistamines, blood pressure medications, nonsteroidal inflammatory drugs, antifungal agents, diuretics, oral diabetes medications, tranquilizers, and tricyclic antidepressants. Photosensitivity can also result from exposure to soaps, deodorants, perfumes, dandruff shampoos that contain coal tar, and even some sunscreens. Photoreactive agents are also found in artificial sweeteners, petroleum products, hair dyes, and common household items like shoe polish and mothballs.

In addition, photosensitivity can be the result of an underlying medical condition, such as systemic lupus erythematosus, an autoimmune disease that mainly affects the skin and joints but can involve other organs as well. Porphyria, a disorder that results from too many porphyrin molecules (derived from chemicals that make hemoglobin) in the blood and urine, can cause it, too. People who have AIDS also may be highly sensitive to light.

Being allergic to the sun is no fun. But if it happens to you, consider the bright side (sorry). Skin cancer and sun damage can take years to show up: PMLE alerts you to the sun's danger right away. We all know that tanning and burning are no longer cool.

When I came off the beach with an itchy, bumpy rash after sunbaking on my dream trip to Jamaica, I did what any sensible person would do. First, I cried. Then, I chalked it up to genetics. Maybe photosensitivity is the body's way of protecting itself. Think of my mother. Her skin may not have that sun-drenched glow. But at age 69--we all should look so good.

Treatment and Prevention

What should you do if you break out with a rash after being out in the sun? Treat it as you would a sunburn. Soothe the affected area with a cool bath or a cold compress and take aspirin or acetaminophen for pain. Then, call a doctor for advice. Your doctor may refer you to a dermatologist to evaluate the rash and monitor the situation. Be sure to tell the doctor what medications you're taking and what substances you've applied to the skin. In some cases, blood or urine tests may be ordered to rule out underlying disease.

Photosensitivity--though not necessarily the existence of an allergy--can be confirmed with a phototest. The standard technique is to expose a small area on the buttocks or lower back to artificial light to see if the rash can be replicated. But for most people a phototest isn't necessary. "When a practitioner is familiar with photosensitivity, it isn't difficult to diagnose," says Epstein.

If it is PMLE, the prescription may be to go out in the sun--gradually. Ask your doctor to recommend a broad-based sunscreen, preferably one that contains total sunblock, such as zinc oxide or titanium dioxide. The purpose of sun exposure is to condition your skin for 20 minutes a day to gradually harden it. Extreme sensitivity to light, however, calls for more drastic measures, such as covering up and staying out of direct sunlight. But most cases of PMLE, though not necessarily curable, can be helped with medications

If your PMLE is severe, a dermatologist may recommend one of the following:

• Beta-carotene. A natural source of vitamin A found in vegetables, such as carrots, it may be prescribed as a dietary supplement to reduce the severity of photosensitive reactions. Beta-carotene can be consumed in large amounts without toxicity, but don't be surprised if your skin (particularly your palms) temporarily turns yellow or orange.

• Hydroxycholoroquine. Generally prescribed to prevent and treat malaria, the medication also may suppress or prevent an inflammatory rash provoked by the sun.

• PUVA (psoralen plus UVA). A special form of ultraviolet therapy than combines medication with UV-A radiation. It is administered for several weeks in the early spring to prevent photosensitive reactions.

• Oral steroids. Oral steroids are used therapeutically to help clear up sun rashes. If you are going on vacation, particularly to a tropical climate, you might want to ask your doctor about prescribing a short course of oral steroids.

PMLE--which shows up a few hours to several days after sun exposure--is not a disease in itself but rather a description of symptoms. The "polymorphic" refers to the fact that rash can take many forms, although in one individual it is usually the same every time it appears. The most common variety of rash consists of pink or raised spots on the arms, chest, and lower legs, areas that are most directly exposed to the sun. It may look like an exaggerated sunburn or a bad case of hives. Sometimes the condition can mimic dermatitis, appearing as blisters and red, scaly patches.

Typically, photosensitivity reactions appear in the spring or early summer and are provoked by the first warm, sunny day. "The most common scenario is that a person gets the rash in May or June, continues to spend time outdoors, and by July, the skin adapts. No more rash. Dermatologists call this a hardening process," says Frank DeLaus, MD, a dermatologist in Utica, New York. Another key time for sun allergies is winter holidays spent in the tropics. Skin that hasn't seen the sun in some time is suddenly exposed to a harsh dose of sunlight.

Carla Cantor is a staff member of Medscape Health by Medscape.

Reviewer: Beth Israel Deaconess Medical Center. Reviewed for medical accuracy by physicians at Beth Israel Deaconess Medical Center (BIDMC), Harvard Medical School. BIDMC does not endorse any products or services advertised on this Web site.