Polymorphous light eruption, also known as polymorphic light eruption, is a rash caused by sun exposure in people who have developed sensitivity to sunlight. The rash usually appears as red, tiny bumps or slightly raised patches of skin.
Polymorphous light eruption occurs most often during spring and early summer when a person's exposure to sunlight increases. Repeat episodes are less likely as the summer progresses. But the rash often recurs each year after the first incident.
Polymorphous light eruption usually goes away on its own without scarring within 10 days. People with severe or persistent rashes may need treatment with medication.
The term "eruption" refers to the rash, which usually appears 30 minutes to several hours after exposure to sunlight. The rash typically appears on areas of the body that tend to be covered during winter but exposed in summer: the upper chest, front of the neck and arms.
Characteristics of the rash may include:
Dense clusters of small bumps and blisters
Red, raised rough patches
Itching or burning
Rarely people may have other signs or symptoms, such as fever, chills, headache or nausea. These conditions may be the result of an associated sunburn rather than polymorphous light eruption.
Treatment of polymorphous light eruption usually isn't necessary because the rash typically goes away on its own within 10 days. If your symptoms are severe, your doctor may prescribe anti-itch medicine (a corticosteroid cream or pill). Treatment is also available to help prevent a rash.
Your doctor may suggest phototherapy to prevent seasonal episodes of polymorphous light eruption in people who have experienced disabling signs and symptoms. Phototherapy exposes your skin to small doses of UVA or UVB light, which helps your skin be less sensitive to light. Basically, it's a controlled version of the increased exposure you would experience over the course of the summer.
One type of light therapy called psoralen plus ultraviolet A (PUVA) combines UVA with a medicine called psoralen, which makes the skin more sensitive to this light. Short-term side effects of this therapy may include nausea, headache and itching.