August 12, 2011
Dear Mayo Clinic:
Can anything be done to treat polymorphous light eruption? Staying indoors all summer isn't an option, but I break out in hives every time I spend time in the sun. Will this damage my skin permanently over time?
Polymorphous light eruption (PMLE) is a skin condition caused by hypersensitivity to ultraviolet light. PMLE can be a painful nuisance but doesn't cause long-term skin damage. For most people, sensitizing the skin to ultraviolet light can reduce or eliminate symptoms. In severe cases, medication to regulate the body's immune system may be necessary to treat PMLE.
PMLE results from an immune system response. When people with PMLE haven't been exposed to ultraviolet light for a while — usually several weeks to several months — and then they are re-exposed to it, their immune system causes a skin reaction. PMLE is most common in fair-skinned people who live in northern climates. It often occurs in the springtime or when people go to a sunny vacation destination during the winter.
Ultraviolet light is an immune stimulus, and the immune system has to adjust to it. People who live in southern climates see ultraviolet light year-round. In northern climates, people tend to stay inside during the winter, and their immune systems can become desensitized to ultraviolet light. When they are re-exposed, the immune system must learn to adjust to that stimulus again. The immune systems of people with PMLE react with a skin rash.
The reaction doesn't appear immediately. Usually the body responds after about 30 minutes to several hours of sun exposure. "Polymorphous" means "many forms," so different people with PMLE get different skin rashes — anything from a prickly, bumpy rash to hives to an eczema-like dermatitis patch. The rash typically appears on parts of the body exposed to the sun, especially the face, neck, arms and hands. The rash lasts several days to weeks, and if you're re-exposed to ultraviolet light during that time, the rash re-erupts.
PMLE isn't dangerous and is not a risk for long-term skin damage. But it definitely causes discomfort. Along with the rash, people who have PMLE often feel a burning and itching sensation on their skin when they are in the sun, making time outdoors uncomfortable.
The best way to combat PMLE for many people is to slowly sensitize skin to ultraviolet light over the course of several weeks. To do this, always apply sunscreen to exposed skin before you go out or wear photoprotective clothing that screens out ultraviolet light with a sun protection factor (SPF) of 55 or higher.
When you first go out after being away from sunshine for a while, limit your time in the sun and avoid the peak hours of sunlight — between 10 a.m. and 4 p.m. You should be able to gradually work your way up to time outside during those hours, but always wear sunscreen. If you can't tolerate sunscreen, consistently wearing photoprotective clothing is an option. Once your skin is sensitized to ultraviolet light, the reaction should be minimal or disappear completely.
If it takes a long time for your skin to become sensitized, or if you have intermittent sun exposure throughout the winter, prescription ultraviolet therapy can help maintain your skin's ultraviolet tolerance. For this therapy, a dermatologist tests your skin to determine what type of ultraviolet light causes a reaction. You are then exposed to a gradually increasing dose of that light in the form of artificial sunlight until your immune system becomes tolerant of it.
If you have severe sensitivity to ultraviolet light and gradual sensitization isn't an option, prescription medication to regulate the immune system may be an effective treatment alternative.
Before you begin sensitizing your skin to ultraviolet light, talk to your dermatologist about PMLE and determine the treatment approach that's right for you.
— Dawn Davis, M.D., Dermatology, Mayo Clinic, Rochester, Minn.