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.