Pityriasis Rosea
Pityriasis rosea is a common viral disease that usually affects individuals between 10-35 years of age. The rash typically lasts six to nine weeks, rarely extending longer than 12 weeks. Once a person has pityriasis rosea, it generally does not recur in their lifetime.

Pityriasis rosea characteristically begins as an asymptomatic single, large pink, scaly plaque called the "herald patch" or mother patch, measuring 2-10 centimeters. The herald patch is a slightly scaly dry pink to red plaque which appears on the back, chest, or neck and has a well-defined, scaly border.

One to two weeks following the initial appearance of the herald patch, those affected will then develop many smaller pink spots across their trunk, arms, and legs. The second stage of pityriasis rosea erupts with a large number of oval spots, ranging in diameter from 0.5 centimeter (size of a pencil eraser) to 1.5 centimeters (size of a peanut). The individual spots form a symmetrical "Christmas tree" pattern on the back with the long axis of the ovals oriented in the "Lines of Blaschko" (invisible skin lines of embryonic origin). This rash is usually limited to the trunk, arms, and legs. Pityriasis rosea usually spares the face, hands, and feet.