What is polymorphic light eruption?
Polymorphic light eruption (PMLE) is a particular rash that occurs in reaction to sunlight on the skin. The name comes from polymorphic eruption, which means a rash that has many forms (it can look different in each person).
PMLE is not infectious (you can’t catch it) and it has nothing to do with skin cancer.
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. Commonly this happens 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. The problem is more common in countries with temperate climates – that is, neither hot like the tropics nor cold. Europe and America have temperate climates.
What causes polymorphic light eruption?
Sunlight contains various types of rays (radiation). The ones which can cause PMLE are ultraviolet (UV) light 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. Sometimes it can occur after exposure to fluorescent lighting.
We do not know exactly how the sunlight causes PMLE, or why some people get PMLE and others don’t. It is most likely to be related to an immune system reaction in the skin, in certain people.
What are the symptoms of polymorphic light eruption?
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 range from mild to severe.
The picture shows a typical rash of PMLE, although it can vary from person to person. The rash is usually on the parts of the body which have been covered during the winter, such as the arms and chest. The face and hands are less likely to be affected.
The rash clears up within a week if you stay out of the sun. However, if there is more sunshine on the skin then it is likely to get worse. It heals well, without scarring. The rash may recur (come back) if you go into strong sun again. However, symptoms tend to improve during the summer, as your skin becomes more adapted to sunlight.
Some people have a more severe form of PMLE which can occur even in winter.
How is polymorphic light eruption diagnosed?
The diagnosis can usually be made by a doctor from the history (description) and typical time course of the rash.
Blood tests or sometimes a skin biopsy are occasionally needed to rule out other conditions. A skin biopsy is where a small sample of skin is removed and examined under the microscope in a laboratory. This means that the cells in the skin can be seen and an accurate diagnosis can be confirmed.
Phototesting is sometimes used to confirm the diagnosis. This involves giving a small area of skin some artificial sunlight-type rays (UV or visible light) and seeing how the skin reacts.
What is the treatment for polymorphic light eruption?
For the rash
The rash normally heals completely within a week if you avoid further sun exposure. Meanwhile, a cream containing corticosteroid will help to settle the rash. Corticosteroids (often just called steroids ) work by reducing inflammation. Hydrocortisone cream is an example of a weak steroid cream that can help ease itching and soreness. Occasionally, and for severe symptoms, a short course of corticosteroid tablets (called prednisolone) is used. Antihistamine tablets can help to reduce itching.
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 sunscreen. Choose sunscreen with a high sun protection factor (SPF) AND a high UVA and UVB protection rating (star system). Apply it frequently throughout the day, particularly after swimming, towelling dry or sweating.
- Be aware that sunscreens do not offer 100% protection. It is still important to cover up (hats, long sleeves) and find shaded areas out of direct sun.
For severe or troublesome PMLE
If the above treatments are not sufficient, other options are:
- Light therapy (phototherapy). This is treatment with UV light, in gradually increasing doses. It helps the skin to become more resistant to PMLE when you go into natural sunshine. Effectively it desensitises you to the sun by preparing your skin for sun exposure. (This treatment is sometimes called photo hardening 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. It is normally given in the spring but its effects wear off, so it has to be repeated every year.
- Hydroxychloroquine. This is a tablet normally used against malaria. It helps to reduce PMLE symptoms, but can have side-effects in some people.
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 beta-carotene.
- 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 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. You may need to take vitamin D supplements if you have very little sunlight exposure over a long period. You can discuss this with your doctor. (See separate leaflet called ‘Vitamin D Deficiency’ for more information.)
What is the outlook for polymorphic light eruption?
Although no treatment gets rid of PMLE forever, 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. Over time you learn how much sun your skin can tolerate, and you should try to keep within that limit to avoid PMLE. You will learn to introduce your skin to sunlight gradually in the spring.
- 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).
Rarely, PMLE may be an early feature of another skin condition called systemic lupus erythematosis (SLE). (See separate leaflet called ‘Systemic Lupus Erythematosus’ for more information.)
A charity dealing with allergy. It has useful fact sheets including one on sun allergy. The term allergy is not correctly used here, but the leaflet is on the subject of PMLE.
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