Polymorphic light eruption is a skin rash that can happen when you go out in the sun.
What is a polymorphic light eruption?
Polymorphic light eruption (PMLE) is a rash which comes on after being in strong sunlight.
- It looks like reddened skin with raised red spots or small blisters.
- It is generally itchy and uncomfortable.
- It can feel sore or burning.
- It occurs most often on areas of skin that haven't seen the sun for a while - it is more common on the arms and the chest than on the face or the hands.
- It can take as little as 20 minutes of strong sun to trigger the rash. The rash generally comes on within a few hours of going into the sun.
- The rash usually gets better within a few days.
- The rash heals completely, without scarring.
The rash can look quite different in different people, although in any one person it usually looks the same each time it comes. It can range from mild to severe.
The rash generally clears up within a week if you stay out of the sun. However, if you get more sunshine on your skin then it is likely to get worse. The rash may 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 even occur in winter or under fluorescent lights.
When does it happen?
PMLE is most likely to occur in spring or early summer when your skin is not used to sunshine, or perhaps when you go on holiday to a sunny place. It can keep coming back as your skin gets used to the sun but is usually less severe each time it appears and it gets better more quickly.
PMLE is not the same as sunburn. See the separate leaflet called Sun and Sunburn.
You can't catch PMLE (it is not infectious) and it has nothing to do with skin cancer. See the separate leaflet called Preventing Skin Cancer.
Who gets it?
Polymorphic light eruption (PMLE) mostly affects people aged 20-40 years. It is more common in women. It probably affects around 1 in 10 European women.
It doesn't only occur in people with pale skin; it can also occur in people with darker skin.
The problem is more common in countries with temperate climates - that is, neither hot like the tropics nor cold. Northern Europe and much of North America have temperate climates.
What causes polymorphic light eruption?
PMLE tends to happen when you go out in the sun in the spring or early in the summer, when your skin is not used to sunshine. It may also happen if you go on holiday to a sunny place. It is thought that in people who get PMLE, there is an immune system reaction in the skin which is triggered by UVA (see below).
Sunlight contains various types of rays (radiation). The ones which can cause PMLE are ultraviolet (UV) light and visible light. UV light has two types, UVA and UVB. While sunburn is caused by UVB, it is UVA which causes PMLE. Unlike UVB, 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 even occur after exposure to fluorescent lighting.
It is not known exactly how the sunlight causes PMLE, or why some people get PMLE and others don't. Some studies have suggested that it is more common in people who smoke or drink six or more alcoholic drinks a week.
How is polymorphic light eruption diagnosed?
The diagnosis of PMLE can usually be made by a doctor from a description of the appearance of the rash and the relationship of the rash to the time of exposure to sunlight.
Generally no tests are needed but sometimes blood tests or a skin sample (biopsy) are taken if the doctor wants to rule out other conditions. If a biopsy is required, a small sample of skin is removed and examined under the microscope in a laboratory. This means the cells in the skin can be seen and an accurate diagnosis can be made.
Photo-testing is sometimes used to confirm the diagnosis. This involves shining some artificial sunlight-type rays (UV or visible light) on to a small area of skin to observe how the skin reacts.
Rarely, PMLE may be an early feature of a condition called systemic lupus erythematosus (SLE).
What might help to protect you from developing polymorphic light eruption?
Prevention is definitely better than cure. If you have had PMLE in the past, you are quite likely to get it again the following year when you start to go out in the sun.
- Sunscreen is helpful to prevent the rash.
- Make sure you use one with a good sun protection factor (SPF) and also protection against UVA and UVB (star system).
- Apply sunscreen frequently during the day, especially after swimming, towelling or sweating.
- Remember that sunscreen doesn't offer 100% protection.
- It is also important to stay out of the sun, especially in the middle of the day, between 11 am and 3 pm.
- Put on a wide-brimmed hat and wear clothes with long sleeves.
Polymorphic light eruption treatment
If you do develop PMLE, there are several things you can try to ease the symptoms:
- A mild steroid cream like hydrocortisone can help the redness to settle down.
- Antihistamine tablets can help to reduce the itching as well.
- If the rash is very severe then a doctor may prescribe a short course of corticosteroid tablets (often just called steroids) such as prednisolone which will help the inflammation to settle.
If you get the rash, you should stay out of the sun as much as possible and the rash should settle within a week. If you go out in the sun while the rash is still there, it is likely to get worse. It may come back if you go out in the sun again but tends to get less severe as the summer progresses and your skin becomes adapted to being out in the sun.
What other treatments are there for polymorphic light eruption?
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).
- Cream containing a form of vitamin D.
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.
What is the outlook for polymorphic light eruption?
Although no treatment gets rid of polymorphic light eruption (PMLE) for ever, 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 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 the age of 50).
Will it ever go away?
Some people get PMLE each year. It starts each spring with a rash that lasts for up to a week, and then comes back if you go out in the sun again. But it is usually less severe each time it comes back.
Further reading and references
; DermNet NZ
; Management of polymorphous light eruption : clinical course, pathogenesis, diagnosis and intervention. Am J Clin Dermatol. 20034(6):399-406.
; Photodermatoses: diagnosis and treatment. Dtsch Arztebl Int. 2011 Mar108(9):135-41. doi: 10.3238/arztebl.2011.0135. Epub 2011 Mar 4.
; Polymorphic light eruption may be associated with cigarette smoking and alcohol consumption. Photodermatol Photoimmunol Photomed. 2006 Apr22(2):87-92. doi: 10.1111/j.1600-0781.2006.00204.x.
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