Polymorphic light eruption (PMLE) is a common skin disease caused by exposure to sunlight, resulting in an itchy red rash that disappears within a week but reappears upon further exposure. The cause is unknown, but it is thought to be an acquired reaction to ultraviolet light. Treatment includes topical corticosteroids, antihistamines, and desensitization therapy. PMLE is not harmful but can be irritating and embarrassing, affecting visible areas of the body. If the rash persists for more than a week, it is advisable to consult a dermatologist.
Polymorphic light eruption (PMLE or PLE) is the most common form of photodermatosis. Photodermatoses are skin diseases caused by exposure to sunlight; the term “sun poisoning” is sometimes used to describe this family of conditions. Although doctors have studied polymorphic light eruption quite extensively, the condition appears to be idiopathic in origin, meaning that no cause has been determined.
Typically, polymorphic light eruption begins under age 30 and is more common in women and residents of the Northern Hemisphere. After exposure to sunlight, the skin develops an itchy red rash, often starting as spots that eventually bond together. Within a day to a week, the rash disappears, but reappears if the patient is exposed to the sun again.
The mechanisms of polymorphic light eruption are not fully understood, but doctors suspect that it is an acquired reaction to ultraviolet light. The condition has been theorized to be caused by compounds in the skin that change in reaction to UV exposure, triggering an immune system response which in turn creates the rash. As the patient ages, the rash can become much more severe with each exposure.
Rashes caused by polymorphic light eruption can be treated with the use of topical corticosteroids and ingested antihistamines, drugs that inhibit the immune system’s reaction. These medications can also sometimes be used to manage the skin’s response to sun exposure. The best treatment for polymorphic light eruption is desensitization therapy, in which the patient is exposed to controlled amounts of UV light for set periods in hopes of desensitizing the body so the reaction doesn’t recur.
This sensitivity to the sun isn’t thought to be harmful, but it can be irritating or embarrassing, as the rash favors the upper chest, arms, and face—all highly visible areas. To keep the rash from recurring, some people like to get treatment, even though it’s generally not necessary. When the rash comes back, it usually clears up on its own. However, if it doesn’t go away within a week, it’s a good idea to see a dermatologist and mention previous episodes of PMLE. Other forms of photodermatosis can sometimes resemble PMLE, so if the diagnosis hasn’t been confirmed, it might be wise to seek the advice of a doctor.
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