What is pityriasis rosea?

Pityriasis rosea is a harmless, 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.

See a picture of pityriasis rosea.

What causes pityriasis rosea?

The cause of pityriasis rosea is unknown. Unlike many other skin conditions, it is not an allergic reaction or caused by a fungus or bacteria. Some experts think it may be caused by a virus. But neither signs of a virus (such as its genetic material) nor symptoms of a viral infection (such as a fever) are found in everyone with pityriasis rosea.

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 to 10 cm. The larger patches are more common. See a picture of a herald patch.
• Days to weeks later, salmon-colored, 1 cm to 2 cm 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 usually does not itch, although there may be mild itching. About 25% of people with the condition have a mild to severe itch.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.

How is pityriasis rosea diagnosed?

Your doctor will diagnose pityriasis rosea by looking at the rash. Diagnosis can be difficult 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.

How is it treated?