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Pityriasis Rosea - Topic Overview

What is pityriasis rosea?

Pityriasis rosea (say "pih-tih-RY-uh-sus ROH-zee-uh") is a common skin problem that causes a rash. Although it can occur at any age, it is seen most often in those between the ages of 10 and 35.

Pityriasis rosea is usually harmless. But it can cause serious problems in pregnant women.

See a picture of pityriasis roseacamera.gif.

What causes pityriasis rosea?

Experts aren't sure what causes pityriasis rosea. Unlike many other skin conditions, it is not an allergic reaction or caused by a fungus or bacteria. And there aren't signs that it is caused by a virus. But something irritates the skin and causes the rash.

What are the symptoms?

Pityriasis rosea causes a rash.

  • The rash often begins with a single, round or oval, pink patch that is scaly with a raised border (herald patch). The size of the patch ranges from 2 cm (0.8 in.) to 10 cm (3.9 in.). The larger patches are more common. See a picture of a herald patchcamera.gif.
  • Days to weeks later, salmon-colored, 1 cm (0.4 in.) to 2 cm (0.8 in.) oval patches appear in batches on the abdomen, chest, back, arms, and legs. Patches sometimes spread to the neck but rarely to the face.
  • Patches on the back are often vertical and angled to form a "Christmas tree" or "fir tree" appearance.
  • The rash does not cause itching in 25% of people who have pityriasis rosea. For 50% of people, the itch is mild to moderate. And for 25% of people, the itch is severe.1
  • The rash usually lasts 6 to 8 weeks, but it can last up to several months.

The rash may take other forms. Rounded bumps (papular rash) may be seen in young children, pregnant women, and people with dark skin. Blisters (vesicular rash) may be seen in infants and young children. In some people, the herald patch may not appear, or two herald patches may appear close together.

Before the herald patch appears, you may feel tired and as though you have a cold. You may have a headache, nausea, sore throat, and loss of appetite.

The pityriasis rosea rash is similar to the rash seen in other skin conditions, including ringworm of the skin, tinea versicolor, eczema, and psoriasis.

A rash similar to pityriasis rosea also can be caused by syphilis and by certain medicines such as antibiotics.

If you get a rash on the palms of your hands or the soles of your feet, see your doctor. This can be a sign of something more serious than pityriasis rosea.

How is pityriasis rosea diagnosed?

Your doctor will diagnose pityriasis rosea by looking at the rash. Diagnosis can be hard when only the herald patch is visible, because the condition is often mistaken for ringworm or eczema at this time. After the rash appears, diagnosis is generally clear.

If the diagnosis is unclear, your doctor may do a potassium hydroxide (KOH) test to make sure the rash is not caused by a fungal infection. A skin sample may be taken from the infected area and examined under the microscope (biopsy). If the diagnosis is unclear in a sexually active person, a test for syphilis is often done.

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WebMD Medical Reference from Healthwise

Last Updated: November 03, 2011
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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