Polymorphous light eruption (PMLE) is an acquired condition, which means that it can develop at any time. PMLE is characterized by itchy, red lesions, occasionally with blister formation, that occur within hours to days of ultraviolet light exposure. Although it can occur in all skin types, it is most common in fair-skinned individuals, with an increased prevalence the greater the distance from the equator. The onset is usually within the first three decades of life, with females being affected two to three times more often than males.
The rash of PMLE typically manifests one to four days after exposure to sunlight. There may be redness and itching during sun exposure, then a rash often develops within the first twenty-four hours. The eruption often begins each spring, particularly during sunny vacations. However, it can occur during the winter from reflected snow, and through window glass. Change in climate may play a role, as one living in a tropical climate may not get PMLE, but then later develop it when relocated to a climate with variable seasons.
Common areas of involvement include the face, upper chest, neck and arms. For most people, the area affected tends to be the same each season. The areas that are often most severely involved are those covered during the winter season. With continued sun exposure, people may clear by summer or autumn.
In mild cases, most people can be managed by sun protection, with the use of broad spectrum sunscreens, sun protective clothing and sun avoidance. For more moderate cases, corticosteroids (topical, and sometimes oral) may be necessary. Antihistamines may be beneficial for itch. The more severe cases may require strong systemic medications that often need frequent monitoring by a physician.
Like many skin conditions, PMLE can mimic other sun sensitizing cutaneous disorders, although it is the most common photodermatosis. A new medication, contact with certain chemicals and plants, and systemic disorders can cause sun sensitivity. Therefore, a thorough evaluation that may include blood work, allergy testing, and a skin biopsy may be warranted.