Pityriasis rosea is a rash that occurs most commonly in the spring and fall in adolescents and young adults.
The rash of pityriasis rosea can often be identified by a single oval patch called the “herald patch.” This herald patch may be slightly scaly and may be mistaken for ringworm or dermatitis.
Over time, more pink spots develop on the arms, legs, and trunk. The patches on the trunk may form a pattern, resembling an evergreen tree with drooping branches.
The spots usually start to fade after 3 to 4 weeks, but may take several months to disappear. Some darker-skinned persons may develop long-lasting flat brown spots (hyperpigmentation).
Some people may experience itching. This can worsen under hot conditions. Physical activity, like jogging or running, or bathing in hot water, may cause the rash to temporarily worsen or reappear. In some cases, the patches will reappear up to several weeks after the first episode. This can continue for many months.
The cause is unknown, but it is not contagious.
The appearance of the rash is usually sufficient for a diagnosis, but in some cases blood tests, skin scrapings, or a biopsy may be necessary.