Pityriasis rosea (say "pih-tih-RY-uh-sus ROH-zee-uh") is a common skin problem that causes a rash.
The rash often begins with a herald patch—a single, round-to-oval, pink patch
that is scaly with a raised border. The size of the patch ranges from 2 cm (0.8
in.) to 10 cm (3.9 in.). A larger patch is more common.
Pityriasis rosea is usually harmless. But it can cause serious problems in pregnant women.
E. Gregory Thompson, MD - Internal Medicine & Randall D. Burr, MD - Dermatology
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