What is polymorphic light eruption?

Polymorphic light eruption is a particular type of rash that occurs in reaction to sunlight on the skin. The name comes from 'polymorphic eruption', which means a rash that varies (it can look different in each person). It will be called PMLE in the rest of this leaflet.

With PMLE, the rash follows a particular pattern (explained below under symptoms). It usually starts when you first get sun on your skin after a long period without much sunshine. For example, in spring, or if you go on a sunny holiday during the winter.

PMLE mostly affects people aged 20-40 years. It is more common in women and in people with fair skin type. It probably affects around 1 in 10 European women.

What causes PMLE?

Sunlight contains various types of rays (radiation). The ones which can cause PMLE are UVA, UVB and visible light. UVA and visible light can pass through glass, so it is possible to get PMLE when exposed to strong sunlight through a window.

We do not know exactly how the sunlight causes PMLE, or why some people get PMLE and others don’t. Possibly, the sunlight produces a change in some chemicals in the skin, which the body's immune system reacts to, causing a rash.

What are the symptoms of PMLE?

The symptom is a rash which comes on after being in strong sunlight. It can take as little as 20 minutes of strong sun to trigger the rash. It usually appears within hours of the sunshine exposure. The rash itself looks like reddened skin with small raised spots or small blisters. It often feels itchy or burning. It can be mild or severe.

How is PMLE diagnosed?

The diagnosis can usually be made by a doctor from the history (description) and typical time course of the rash.

Tests may be needed to rule out other conditions. For example, blood tests or sometimes a skin biopsy. (A skin biopsy means taking a tiny sample of skin using local anaesthetic.)

‘Phototesting’ is sometimes used to confirm the diagnosis. This involves giving a small area of skin some artificial sunlight-type rays (ultraviolet or visible light) and seeing how the skin reacts to these.

What is the treatment for PMLE?

For the rash

The rash normally heals completely within a week if you avoid more strong sunshine. Meanwhile, a cream containing ‘corticosteroid’ will help to settle the rash. Corticosteroids work by reducing inflammation. For severe symptoms, a short course of corticosteroid tablets is sometimes used. Antihistamine tablets can help reduce itching.

Prevention

Usually, symptoms can be controlled by gradually building up the amount of sunshine on your skin. In order to do this, you will need to control your sunshine exposure by:

• Staying out of the sun, especially between 10 am and 3 pm when the sun is strongest.
• Wearing sun-protective clothing, such as long sleeves and a broad-brimmed hat.
• Using sun block (sunscreen) cream. Choose one with a high sun protection factor AND a high UVA protection rating. The best type is one which is 'broad spectrum' (screens out a wide range of the sun's rays) and 'semi-opaque' (screens out some of the visible light). Use the sunblock several times a day.
• Be aware that sunblocks may not screen out all the UVA and visible light - therefore the other advice is also important (protective clothing and staying out of the sun).

For severe or troublesome PMLE

If the above treatments are not sufficient, other options are:

• Light therapy (‘phototherapy’). This is treatment with ultraviolet light, in gradually increasing doses. It helps the skin to become more resistant to PMLE when you go into natural sunshine. (This treatment is sometimes called ‘photohardening’ which means increasing the skin’s resistance to light - not actually making the skin hard). The treatment is usually given in a hospital outpatient department.
• Hydroxychloroquine. This is a tablet normally used against malaria. It helps to reduce PMLE symptoms, but can have side-effects.

Research

Various other treatments have been tried, and might have a role in helping PMLE, although they are not standard treatment at present. These are:

• Special sunscreens with high UVA protection.
• Cream containing sunscreen plus antioxidants (alpha-glucosylrutin and vitamin E).
• Tablets containing ‘carotenoids’ such as betacarotene.
• Vitamin supplements (vitamin E or nicotinamide).
• Azathioprine tablets (medication affecting the immune system, which may have serious side-effects).

A note about vitamin D

If your PMLE makes you avoid sunlight to a large extent, you may be at risk of getting a type of vitamin deficiency called ‘vitamin D deficiency’. This is because most of the body’s vitamin D is made by the action of sunlight on skin, and it needs outdoor sunlight, without sunscreen, to make vitamin D. If you are getting very little sunlight for a long time, you may need to take vitamin D supplements. You can discuss this with your doctor. See separate leaflet called 'Vitamin D Deficiency' for more detail.

What is the outlook for PMLE?

The outlook is good. The rash heals completely, although while it lasts it may be uncomfortable or unsightly.

In the longer term:

• For most people, PMLE tends to follow a pattern, and it usually recurs (comes back) each year when you first get exposed to strong sunshine.
• For some people, PMLE may improve or clear up completely over the years.
• PMLE also tends to improve for women after the menopause (when menstrual cycles stop at around age 50).

Occasionally, PMLE can be an early feature of another skin condition called lupus erythematosis – but this is rare.