Polymorphic Light Eruption

 What is PLE?

 The term ‘light eruption’ is easy to understand - a rash that comes up after exposure to light. ‘Polymorphic’ is more difficult. ‘Poly’ means ‘many’, and ‘morphic’ means ‘forms’. In other words, the rash of PLE can take many different forms, including small red bumps, larger red areas, and blisters. In PLE, a rash with one or more of these components comes up a day or two after exposure to the sun. PLE is common, perhaps affecting up to 10% of the population. It tends to appear in the spring.   



What causes PLE?


PLE is a response to sunlight. As little as 20 minutes of strong sun can trigger it. PLE can come up even when the light has passed through window glass, and sometimes even after exposure to fluorescent lighting. Both long (UVA) and short (UVB) wavelengths of ultraviolet light can cause PLE in a susceptible person, but it is still not clear how they trigger the rash. An immunological reaction seems the most likely explanation.


Most people with PLE get it in the spring after they go out in the sun. Often it comes up on a holiday abroad, and sometimes it clears up before they return home. The rash tends to affect areas that have been covered by clothing during the winter. It goes away without treatment in about a week if there is no further sun exposure. If you stay in the sun, the rash will get worse and spread; but as the summer wears on, the skin becomes resistant to sunlight and more of it is needed to provoke the rash.


Other points about PLE:


  • Women get PLE more often than men. 
  • It usually starts under the age of 30.
  • It affects people with all types of skin but is most common in those who are fair. 
  • It is most common in countries where the climate is temperate, and exposure to the sun is usually not heavy.
  • It is not infectious and has no connection with skin cancer.

Is PLE hereditary?

Probably not, although about 15% of those who have PLE know of other family members who have it too.


What are the symptoms of PLE?


  • The rash of PLE can itch or feel like a burn.
  • PLE can be embarrassing as it comes up on exposed areas.
  • It restricts outdoor activities and holidays in the sun.

What does PLE look like?


  • PLE ranges from a mild rash that lasts for only a short time to a severe and extensive eruption that spoils the quality of life.
  • The rash comes up equally on both sides of the body, affecting mainly those parts of the skin that are kept covered in the winter – such as the arms and the upper trunk. For this reason the face and the backs of the hands are sometimes, but not always, spared. 
  • The appearance of the rash varies from person to person. The most common type has large numbers of small red bumps. In other people the rash is made up of larger red areas and small blisters. The rash of each affected person usually looks the same every time it comes back.  
  • When the rash settles, it does so without leaving scars.

How will PLE be diagnosed?

Your general practitioner may refer you to a skin specialist who will base the diagnosis of PLE on the appearance of the rash and the story that it has been provoked by sunlight. Tests will be done to rule out other conditions that can cause sun sensitivity, such as lupus erythematosus. Phototesting (trying to reproduce the rash by testing the skin with different amounts and wavelengths of ultraviolet and visible light) is sometimes helpful too.


Can PLE be cured?


No treatment will get rid of PLE forever. However, many people remain clear if they avoid exposure to the sun and use an effective sunscreen. The tendency to get PLE may go away by itself after a few years.


To find out about available treatments, please see this page on the British Association of Dermatologists website, and for further reading on PLE, please click here. 

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