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
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
- 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
- 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"
- 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
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,
A rash similar to pityriasis
rosea also can be caused by
syphilis and by certain medicines such as
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?
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
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