Slide show: Common skin rashes

Christmas tree rash (pityriasis rosea) is a fine, itchy, scaly rash that usually appears first as a single patch on the chest, abdomen or back. This rash (herald patch) may spread as small patches to other parts of the back, chest and neck. The rash may form a pattern on the back that resembles a Christmas tree.

Pityriasis rosea usually goes away without treatment in four to 10 weeks, but it can last months. Medicated lotions may lessen itchiness and speed the disappearance of the rash. Often, though, no treatment is required.