Polymorphous light eruption is a rash caused by sun exposure in people who have developed sensitivity to sunlight. The rash usually appears as tiny, inflamed bumps or slightly raised patches of skin.
The reaction usually happens during spring and early summer when exposure to sunlight increases. It's less likely to be repeated as the summer progresses. But the rash often happens again each year after the first time. If you're going to develop this sensitivity, the first instance will likely be in your teens or 20s.
The condition is also known as polymorphic light eruption, sun allergy and sun poisoning.
Polymorphous light eruption usually goes away on its own without scarring within 10 days. People with severe or persistent rashes may need medication.
Symptoms of the rash in polymorphous light eruption may include:
- Dense clusters of small bumps and blisters
- Inflamed, raised rough patches
- Itching or burning
People may rarely have other symptoms such as fever and chills.
In polymorphous light eruption, eruption refers to the rash, which usually appears 30 minutes to several hours after sun exposure. The rash usually appears on areas of the body that are covered during winter but exposed in summer such as the upper chest, front of the neck and arms.
When to see a health care provider
See your health care provider if you have any rash with no obvious cause, such as a known allergy or recent contact with poison ivy.
Polymorphous light eruption rashes look similar to rashes caused by other diseases, some of which are serious. So it's important to get a prompt diagnosis and treatment.
Seek immediate medical care if your rash is:
- Accompanied by fever
The exact cause of polymorphous light eruption isn't understood. The rash appears in people who have developed sensitivity to sunlight, especially ultraviolet (UV) radiation from the sun or other sources, such as tanning beds. This is called photosensitivity. It leads to immune system activity that causes a rash.
UV radiation is a wavelength of sunlight in a range too short for the human eye to see. UV light that reaches the earth is divided into two wavelength bands — ultraviolet A (UVA) and ultraviolet B (UVB).
A person with photosensitivity can react to both types of UV radiation. UVB doesn't penetrate glass. UVA does. Exposure to sunlight through windows or even sunscreen-protected skin may cause a reaction in some people with photosensitivity.
With polymorphous light eruption, sensitivity to sunlight lessens with repeated exposure. Features of polymorphous light eruption are somewhat predictable:
- An episode is most likely to occur after the first one or two times of sun exposure after a long period of no exposure, such as in spring or early summer.
- Episodes are less likely to happen as the summer progresses.
- After the first episode, it's likely to happen each year. Some people gradually become less sensitive over several years and eventually no longer experience the yearly rash.
Anyone can develop polymorphous light eruption, but several factors are associated with an increased risk of the condition:
- Being female
- Having skin that sunburns easily
- Living in northern regions
- Having a family history of the condition