Picture of Pityriasis Rosea 2

Pityriasis rosea. Pityriasis rosea is a rash that usually appears on the torso, upper arms, thighs or neck. This rash is thought to be caused by a virus. Even though it is benign, it can cause substantial discomfort and itching. It is easily treated with oral antihistamines or topical steroids to decrease the itching, but can take several weeks to clear up.