Polymorphous light eruption

Polymorphous light eruption, also known as polymorphic light eruption, is an itchy rash caused by sun exposure in people who have developed a sensitivity to sunlight (photosensitivity). The rash usually appears as red, tiny bumps or slightly raised patches of skin.

Polymorphous light eruption occurs most often during spring and early summer when a person's exposure to sunlight increases. Repeat episodes are less likely as the summer progresses, but polymorphous light eruption often recurs each year after the first incident.

Although polymorphous light eruption usually goes away on its own without treatment, medications may be needed to treat severe or persistent cases. Measures to protect the skin from sun exposure or light therapy may help prevent recurring episodes of polymorphous light eruption.

Symptoms Causes Risk factors

The term "eruption" refers to the rash, which usually appears within minutes to hours — or sometimes within a couple of days — after exposure to sunlight. The rash usually appears on areas of the body that tend to be covered during winter but exposed in summer: the upper chest, front of the neck and the arms.

Characteristics of the rash may include:

  • Dense clusters of small bumps
  • Raised rough patches
  • Redness
  • Itching or burning
  • Blistering and swelling (less common)

Rarely people may have other signs or symptoms, such as fever, chills, headache or nausea. These conditions may be the result of an associated sunburn rather than polymorphous light eruption.

When to see a doctor

See your doctor if:

  • You have any rash with no obvious cause, such as a known allergy or known exposure to poison ivy

A number of conditions — including some serious diseases — can cause skin rashes with similar appearances. It's important to get a prompt diagnosis and appropriate treatment.

Seek immediate medical care if your rash is:

  • Widespread
  • Painful
  • Accompanied by fever

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