What is polymorphic light eruption?

Polymorphic is a common photosensitive dermatosis. Approximately 10 – 20 % of the population will get polymorphic light eruption, and women are 6 times more likely to get it than men. It is also more common in people with lighter skin. It tends to first appear in late adolescence or early adulthood, particularly during spring or summer, after exposure to both UVA and UVB radiation. Polymorphic light eruption is covered in more detail in another article.

The lesions in polymorphic light eruption tend to be variable, as the term “polymorphic” suggests. The rash can start within hours of sunlight exposure and can take 5 – 10 days to clear. Most commonly, you will find papules (raised bumps on the skin), which are red in colour and a few millimetres across. Sometimes you can find larger lesions or blisters too. They most commonly appear on the arms, legs, and chest, but not on the face. They can be itchy, but they will resolve without scarring.

Mild cases can be treated by avoiding sunlight. This might involve wearing more clothing or broad-spectrum sunscreens or remaining indoors most of the time. More severe cases can be treated by desensitisation therapy – the skin is exposed to UV light, with or without drugs. This builds up the skin's natural protection. In even more severe cases, steroid creams or antihistamies may be needed. Lotions may be helpful in reducing the itchiness.

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