Pityriasis rosea is a rash of unknown cause which lasts about six weeks. Pityriasis rosea most often affects teenagers or young adults. In some cases there are no other symptoms, but it often follows a few days after a upper respiratory viral infection (cough, cold, sore throat or similar).
A single scaling patch (the herald patch) appears one to twenty days before the general rash. It is an oval pink or red plaque 2-5 cm in diameter, with a scale trailing just inside the edge of the lesion. The herald patch is often mistaken as ringworm. It can also be confused with psoriasis.
A few days later, more scaly patches (flat lesions) or plaques (thickened lesions) appear on the chest and back. A few may also appear on the thighs, upper arms and neck but they are uncommon on the face or scalp. These secondary lesions tend to be smaller than the herald patch. They are oval in shape with a dry surface. Like the herald patch, they may have an inner circlet of scaling. These lesions follow the relaxed skin tension lines (Langers lines) on both sides of the upper trunk so that the rash has been described as looking like a fir tree.
Pityriasis rosea may be very itchy, but in most cases it doesn't itch at all. In white skin the patches are pink or red, but in darker skin they may be pigmented or they may appear white due to the scale.
The lesions of pityriasis rosea are sometimes more prominent in the skin folds than elsewhere on the trunk. A herald patch is followed by oval pink scaly or moist plaques appearing in armpits and groin.
Pityriasis rosea may be set off by a viral infection but it does not appear to be contagious. Herpes viruses 6 and 7, influenza viruses and vaccines have been associated with pityriasis rosea in some cases. The rash may be a reactive response to these or other viruses.
Pityriasis rosea clears up in about six to twelve weeks. Pale marks or brown discolouration may persist for a few months in darker skinned people but eventually the skin returns to its normal appearance.
Second attacks of pityriasis rosea are uncommon, but another viral infection may trigger recurrence years later.
General advice. The rash is irritated by soap; bathe or shower with plain water and bath oil, aqueous cream, or other soap substitute. Apply moisturizing creams to dry skin.
If the rash itches, treatment with a steroid cream or ointment usually brings prompt relief. The steroid probably does not speed up clearance of pityriasis rosea but it reduces the discomfort.
Oral erythromycin has also been reported to help, probably because of a nonspecific anti-inflammatory effect. There have been some reports that aciclovir may be effective.