Pityriasis rosea is a rash of scaly, pink plaques that is harmless and goes away without treatment. It is thought to be caused by a viral infection, but is not contagious.
Most people who develop pityriasis rosea will not get it a second time, probably because they build immunity (resistance) to the virus.
Before the rash starts, an initial patch of red, scaly skin appears, usually on your chest or back. This is known as the 'herald patch'.
The rash that follows the herald patch may look alarming, but the worst problem is that it may be itchy. See Symptoms for more information.
How common is it?
Pityriasis rosea is a common condition, especially in winter, and mainly affects people aged between 10 and 35.
Outlook
Pityriasis rosea will go away on its own without treatment after about eight weeks. It does not leave a scar.
Continue to next section: Symptoms of pityriasis rosea