Warm weather and sunshine have finally arrived in Toronto, and this time of year I am once again seeing patients with a common and frustrating rash...one that is caused by exposure to the sun. If you have enjoyed one or two warm spring days outdoors, only to find that hours later you have developed an intensely itchy, uncomfortable red rash, you may have a sun allergy known as polymorphous light eruption (PMLE).
PMLE is an exaggerated response to sunlight that occurs in about 10% of the population. It is a form of photosensitivity; a reaction to sunlight that characterizes a group of skin conditions in which rashes and sunburns develop or worsen as a result of sun exposure. Of the various types of sun allergy, polymorphous light eruption is the most common. While not dangerous, PMLE episodes can be alarming and uncomfortable, and can put a serious cramp in a spring weekend or a winter vacation.
What Does PMLE Look Like?
PMLE rashes are not sunburns. They are allergic reactions that occur with sun exposure, and often with less sun exposure than is required to burn. PMLE can take many different forms, but is most often seen as itchy, red bumps and patches that develop minutes to hours after sun exposure. It commonly affects the arms, chest, neck, lower legs and feet. The face is often spared, because year-round exposure of the skin on our face means that it is accustomed to the sun. PMLE rashes tend to be intensely itchy and uncomfortable, and usually take several days to a week to resolve on their own.
Polymorphic light eruption can be seen in people of all backgrounds, but is more common in women and in those living in northern climates. It often starts in one's twenties or thirties, but can affect individuals of all age groups. Episodes tend to occur with the first one or two sun exposures of the spring, and tend to wane with ongoing sun exposure over the summer, as the skin develops tolerance to sunlight. PMLE then tends to recur each spring or with winter vacations down south.
Is PMLE Dangerous?
No. In rare cases, the rash can be associated with mild fever, headache or nausea, but there are no known serious health consequences of PMLE outbreaks.
What Causes PMLE?
The exact cause of PMLE isn't well-understood. It is thought to be a type of allergic response to ultraviolet radiation (UVR). Susceptibility to PMLE appears to be genetic, meaning that one may inherit a tendency to develop this skin condition.
Ultraviolet radiation (UVR) that comes from the sun is generally divided into shorter UVB rays and longer UVA rays. Most people with PMLE are allergic to longer UVA rays, although some are allergic to UVB rays and some are allergic to both UVA and UVB. UVA rays penetrate most types of window glass, and so people with PMLE may get a reaction after sitting next to a window.
How Do I Know If I Have PMLE?
If you breakout in a rash after sun exposure (or at any other time!), get an opinion from a dermatologist. There are over a dozen skin conditions that may be caused or aggravated by sun exposure; please do not self-diagnose.
Are There Other Types of Sun Allergy?
Yes. Less common forms of sun allergy include solar urticaria, actinic prurigo and chronic actinic dermatitis. There are also a number of skin conditions, including conditions such as rosacea and lupus, that are not caused by the sun but tend to worsen with sun exposure.
Can PMLE be prevented?
Sometimes. The generous application of a broad-spectrum sunscreen with a high SPF and good UVA coverage may prevent some episodes of PMLE. When choosing a sunscreen, look for ingredients such as avobenzone (Parsol 1789), ecamsule (Mexoryl SX), bisoctrizole (Tinosorb S), Bemotrizinol (Tinosorb M) and/or zinc oxide. In Canada, the Anthelios, Vichy, Ombrelle and Bioderma brands often contain these ingredients. Look for a sunscreen with an SPF of 50 or higher, and remember to reapply your sunscreen every two hours when outdoors, and more frequently if immersed in water or after vigorous exercise.
Sun-protective clothing is often more effective than sunscreens in minimizing or preventing a PMLE outbreak. Clothing with an UPF value above 40 is readily available from numerous retailers, and dark-coloured clothing with a dense weave can serve a similar purpose. Unfortunately, this means that sunbathing without sunscreen in your bikini is out.
Polypodium leucotomos extract is a plant-derived antioxidant that may be helpful in reducing the risk of a PMLE episode. It is sold over-the-counter as a dietary supplement in some countries. Products containing polypodium leucotomos extract have been estimated to provide an SPF of about 3 and are meant to complement, NOT to replace sunscreen and sun-protective clothing.
Can PMLE Be "Cured"?
No. Unfortunately, there is no cure for PMLE at this time. The good news is that for many people, PMLE improves over time. One long-term study found that in almost 60% of people the condition improved or resolved over a period of 16 years (yes, I know that is a really long time).
What Can I Do If I've Developed a PMLE Rash?
PMLE rashes can be very itchy and uncomfortable. Staying cool can be helpful: many people find that cool showers and cool compresses soothe itch. Your dermatologist can prescribe cortisone creams that can improve your symptoms.
How Is PMLE Treated?
Mild cases of PMLE can be prevented by sun protection and sun-avoidance. (see above for what to look for in a sunscreen). Topical cortisone creams can help to improve symptoms.
Phototherapy (the medical use of ultraviolet light) may prevent or minimize PMLE outbreaks. This treatment involves exposing the skin to a portion of the ultraviolet light spectrum that is emitted by a medical device. Approximately 15 sessions, usually given 2-3 times per week in the spring, is generally effective for several months.
Short courses of steroids (by mouth), can be taken during vacations, or a steroid can be given by injection into the muscle prior to a vacation. Each of these medications has side effects that should be thoroughly discussed with your doctor.
Is There Any Good News?
Maybe. One small study has found that those with PMLE may have a reduced risk of skin cancer....perhaps a benefit of hiding from the sun while your friends bake on a beach.