Is It Possible to Have a Sun Allergy?

Understanding Photodermatoses and True Sun Allergy

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People regularly get allergies from things like pollen, pet dander, peanuts, latex, and shellfish, but the one that would seem unlikely is an allergy to sunlight. However, researchers are now just starting to understand how common sun allergies—more accurately referred to as photodermatoses—really is.

In fact, a 2011 study from the Universität Witten-Herdecke Center of Dermatology in Germany suggested that as many as 20% of people in the United States., Scandinavia, and Central Europe has experienced the most common form of the disorder known as polymorphous light eruption (PMLE).

Symptoms

All told, there are well over 20 different types of photodermatoses ranging in severity from mild and transient to life-threatening. Symptoms include:

  • Hives
  • Redness and itching
  • Diffused bumps on exposed skin or raised patches of bumps
  • Blisters
  • Areas of scaling and crusting

This is not to say that all skin reactions to the sun are true allergies. While some people do, in fact, have hypersensitivity to sunlight, other "sun allergies" are caused by medications or topical substance that cause a reaction on the skin when exposed to sunlight.

Causes

Scientists are not entirely sure why people experience reactions to the sun but believe that genetics play a key role. As with all allergies, photodermatoses is caused when an otherwise harmless allergen—in this case, sunlight—triggers an abnormal immune response.

Ultraviolet (UV) light appears to be the culprit. It can cause either a photoallergic reaction (a true allergy involving the immune system) or a phototoxic one (a chemically induced skin reaction, requiring light, that does not involve the immune system).

There are over 20 different types of photodermatoses. Some are common and others are rare. These include sun-induced skin reactions in people with known autoimmune disorders such as lupus) and chronic skin conditions that worsen when exposed to light.

Polymorphous Light Eruption

Polymorphous light eruption (PMLE) is the most common type of photodermatoses. It is called polymorphous because the appearance of the skin reaction can vary from person to person.

PMLE skin lesions typically develop several hours to days after sun exposure. They will appear as raised, reddened patches accompanied by itching and sometimes burning.

They will often become papular in nature (characterized by raised bumps with no visible fluid). The rash will develop most commonly on the upper chest, upper arms, backs of the hands, thighs, and the sides of the face.

The lesions usually disappear spontaneously within several days and do not leave behind any traces. Oral antihistamines can help relieve itching but do little to improve the actual rash. In most cases, time alone will resolve the condition. PMLE is not considering life-threatening.

Solar Urticaria

Solar urticaria is a chronic form of sun-induced photodermatoses. People with this condition will experience itching, redness, and hives on the areas of skin exposed to sunlight. While symptoms are sometimes confused with a sunburn, solar urticaria can develop within minutes and goes away much quicker (usually less than a day) after the sun exposure has stopped.

Solar urticaria is rare but can be life-threatening in some cases. People have been known to experience a deadly, all-body allergic reaction, known as anaphylaxis, in response to sun exposure.

If anaphylaxis is suspected, emergency medical attention should be sought. If left untreated, anaphylaxis can lead to respiratory failure, seizures, shock, coma, and even death. Avoidance of the sun is the best means of protection.

Cholinergic Urticaria

Cholinergic urticaria, more commonly known as heat rash, is a form of hives caused by an increase in body temperature. This not only includes exposure to sunlight but anything that can raise the body temperature as a whole, including hot showers, exercise, spicy foods, or being overheated at night.

The best treatment for cholinergic urticaria is antihistamines. While any antihistamine is likely to help, older ones, such as hydroxyzine, seem to work best.

Cholinergic urticaria is differentiated from PMLE and solar urticaria in that the reaction is not triggered UV rays but by temperature. Even strong emotions can trigger cholinergic urticaria in that they raise body temperature ever so slightly.

Sunscreen Allergy

While contact dermatitis to sunscreen is not as common as an allergy to cosmetics, it is actually not all that uncommon. Known as photo-contact dermatitis, the condition is characterized by a reaction to a topical agent (such as sunscreen, insect repellent, lotions, or fragrances) only when it is exposed to UV light.

The skin reaction can occur on any part of the body where the substance is applied but is usually more pronounced on areas of sun-exposed areas. These include the face, the “V” area of the upper chest and lower neck, the backs of the hands, and the forearms.

Photo-contact dermatitis is considered a phototoxic even in that the reaction would not occur if the sunscreen was not used. Avoidance of the product is the best course of treatment for this condition.

Treatment

Most cases of sun allergy resolve on their own with time. Skin balms such as calamine lotion and aloe vera can help alleviate discomfort, particularly if scaling or crusting occur. Pain can often be treated with a nonsteroidal anti-inflammatory drug like Advil (ibuprofen). More severe cases may require systemic or topical steroids to help bring down the swelling.

Whatever the cause, people with a known sun allergy should make every effort cover up or stay indoors whenever the sun is at its strongest. Sunscreen rarely provides protection from photodermatoses and, in some cases, can make it worse.

When to Call 911

Seek emergency care if some or all of the following occur after sun exposure:

  • Severe rash or hives
  • Shortness of breath
  • Wheezing
  • High fever
  • Fast or irregular heartbeat
  • Nausea and vomiting
  • Confusion
  • Swelling of the face, throat or tongue
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Article Sources

  • Lehmann, P. and Schwarz, T. "Photodermatoses: Diagnosis and Treatment." Dtsch Arztebl Int. 2011; 108(9):135-141. DOI: 10.3238/arztebl.2011.0135