Polymorphic light eruption (PLE): symptoms, treatment and prevention

The NHS says polymorphic light eruption usually does not need any treatment. If symptoms get worse or do not go away, treatments you may have include steroid tablets or medicines applied to the skin (topical corticosteroids), antihistamines and phototherapy (light therapy). A pharmacist can recommend emollients and antihistamines, and your GP may treat you or refer you to a dermatologist.

BAD says most cases are mild and respond to prevention: avoiding intense sun exposure, wearing sun-protective clothing and hats and broad-spectrum sunscreen protecting against both UVA and UVB. Mild rashes can be treated with topical or oral corticosteroids and oral antihistamines may help the itching.

If PLE is very troublesome, BAD describes desensitisation (hardening) treatment: raising the skin's resistance by treating it with increasing doses of ultraviolet light in a phototherapy cubicle, given in the early spring so the skin is ready for the summer sun. The effect wears off in winter, so it is repeated every spring. For a few people with severe PLE, BAD lists hydroxychloroquine, a short course of oral steroids to cover a holiday, or alternatives such as azathioprine as options a specialist may consider.

The main symptom is a rash. The NHS says it usually appears within a few hours or days of going in the sun. The rash may have small raised spots or blisters, or larger blotchy areas, and may be itchy or feel like it is burning. It may be red or pink, which can be harder to see on brown or black skin.

It can appear anywhere on the body but is often in places that are not regularly exposed to the sun, such as the arms, legs or chest. BAD says it is typically symmetrical, affecting areas covered by clothing during the winter, such as the arms, upper thighs and upper trunk, and sometimes the face, neck and backs of the hands. The rash looks the same shape and colour each time.

A similar rash on the ears, called juvenile spring eruption, can cause small itchy or uncomfortable blisters, and the NHS says boys aged 5 to 14 are more likely to get it. The NHS notes polymorphic light eruption can be similar to heat rash (prickly heat).

BAD explains that polymorphic means the rash can take many different forms, including small red bumps, larger red areas and blisters. It is the most common rash caused by ultraviolet (UV) light and tends to be more common in spring and early summer. It is a reaction of the skin to sunlight, and BAD says it might be related to the immune system.

Severe PLE can have a significant psychological impact, which can lead to anxiety and depression, according to BAD.

The NHS says it is caused by a reaction to sunlight, and is more likely when your skin is exposed to strong sunlight for the first time in a while, such as in spring or early summer, or when visiting a sunny country. As summer goes on, the skin becomes more used to sunlight and it is less likely to happen.

BAD says as little as 20 minutes of sun can trigger the rash, that it can appear even when sunlight has passed through window glass and sometimes after exposure to fluorescent lighting, and that it is mainly caused by UVA but UVB and visible light can also do it. About 15% of people with PLE know of other family members who have it.

The rash usually goes away in around a week if you stay out of the sun, but the NHS says it can last longer or get worse if you continue to go in the sun, and may come back when the skin is exposed to sunlight again.

BAD says no medication can cure PLE, but many people do not have a recurrence if they avoid sun exposure and use an effective broad-spectrum sunscreen, and the tendency may go away by itself after a few years as the skin adapts to sunlight.

The NHS advises taking antihistamines if the rash is itchy, applying calamine lotion or emollients to keep the rash cool, staying out of the sun especially between 11am and 3pm, using sunscreen with SPF 50 or more and wearing a sun hat and protective clothing. Apply sunscreen 15 to 30 minutes before going out and reapply every 2 hours and after swimming.

BAD adds wearing long-sleeved, loose-fitting clothing, protecting any rash from further sun, and notes that gradual exposure to sunlight in the spring may help reduce severity in mild PLE. People who avoid the sun may be at risk of low vitamin D, and BAD suggests considering a check of vitamin D levels and, if low, supplements of 10 to 25 micrograms a day, with advice from a GP.

BAD says a dermatologist bases the diagnosis on the appearance of the rash and the history that sunlight caused it. If there is doubt, tests can rule out other conditions that cause sun sensitivity, and photo-testing, which tries to reproduce the rash with different amounts and wavelengths of light, is sometimes needed to exclude other rare types of sun sensitivity.

The NHS says to see a GP if you or your child have or might have polymorphic light eruption and the rash is getting worse or has not got better after 1 week, the rash is swollen, or you also have joint and muscle pain or extreme tiredness. These features need checking because other conditions can cause a sun-triggered rash.

Most people manage PLE with pharmacy advice, sun protection and sometimes a GP prescription. The NHS says your GP may refer you to a dermatologist if it is troublesome, and phototherapy desensitisation is delivered in NHS dermatology phototherapy units, usually in early spring. Private dermatology and phototherapy are also available and follow the same approach; sunscreen and clothing remain the foundation either way.