Illustration copyright 2004 by Nucleus Communications, Inc. All rights reserved. http://www.nucleusinc.com

Pityriasis rosea is a harmless, 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.