Polymorphic Light Eruption

What is polymorphic light eruption?

Polymorphic light eruption (PLE) is an itchy rash brought on by exposure of the skin to sunlight. Light eruption means a rash brought on by light, and polymorphic means that it can take many different forms, from small red bumps to larger patches and, occasionally, blisters. It is the most common rash triggered by ultraviolet (UV) light.

Who gets it?

PLE is very common, affecting an estimated 10 to 20 in 100 people in western countries. Women are affected more often than men, and it frequently becomes less severe after the menopause. Onset is usually before 30, although it can start at any age.

It is most common in people with fair skin, although it can affect any skin type. It is more common in people who live in places with milder sun, such as northern Europe, which is why many people first notice it on holiday.

What causes it?

PLE is mainly triggered by long-wave ultraviolet A (UVA) light, with ultraviolet B (UVB) and visible light playing a part in some people. Even 20 minutes in the sun may be enough to trigger the rash. Because UVA passes through glass, it can even appear after sitting by a window or in a car. Rarely, fluorescent lighting can trigger it.

Why it happens is not completely clear. The likely explanation is that the immune system overreacts to substances that form in the skin after sun exposure.

PLE is most common in spring and early summer, when the skin has had little sun over the winter.

Is it hereditary or contagious?

About 15 in 100 people with PLE have a family member who is also affected, so there is an inherited tendency. It is not contagious.

What does it look and feel like?

The rash appears between a few hours and a few days after sun exposure. It is usually itchy and can also burn or sting. It typically affects both sides of the body evenly, on areas that are covered up during the winter but exposed in spring and summer, such as the arms, the V of the neck, the upper chest and the upper thighs.

On lighter skin, the rash looks pink or red, with small bumps, larger raised patches or small blisters. On brown and black skin, it often appears as many tiny pinpoint bumps that may be skin-coloured or darker than the surrounding skin.

With no more sun, the rash normally clears in 7 to 10 days and leaves no scars.

How is it diagnosed?

PLE is usually diagnosed from the appearance of the rash and its relationship to sun exposure. Photographs taken when the rash is present can be very helpful. If the diagnosis is uncertain, specialist light testing (phototesting) may be used to rule out other light-sensitive conditions, such as lupus, solar urticaria or reactions to medicines. Blood tests are sometimes recommended for the same reason.

What are the treatment options?

Dr Mounsey will confirm the diagnosis and exclude other light-sensitive conditions, sometimes with blood tests. Management is based on careful sun protection, using clothing, shade and a high-factor broad-spectrum sunscreen with good UVA protection. Flares can be settled with steroid creams and antihistamines, and steroid tablets may occasionally be given for a few days for holidays or severe episodes. For people who are badly affected each spring, a course of phototherapy before the summer, known as desensitisation or hardening, may be recommended and can be arranged.

What is the outlook?

PLE cannot be cured, but it often improves over time, with around 6 in 10 people finding it better or gone within 15 years, and with careful sun protection it can usually be well controlled. In many people the rash is worst in spring and becomes less of a problem as the skin gets used to the sun over the summer.

More information

British Association of Dermatologists patient leaflet: https://www.bad.org.uk/pils/polymorphic-light-eruption

This page gives general information only and is not a substitute for a consultation. Everyone's skin is different, and what is right for you will depend on your own circumstances. If you are worried about a skin problem, please book an appointment with Dr Mounsey or speak to your GP. If you have a mole or skin lesion that is changing, bleeding or growing quickly, please seek medical advice promptly.