Answer: The cause of pityriasis rosea is uncertain. Some doctors believe that pityriasis rosea is caused by a viral or bacterial infection. Certain medicines also can cause this rash. Pityriasis rosea is not contagious, so people with this rash do not have to be kept away from other people.http://familydoctor.org/online/famdocen/...The exact cause of pityriasis rosea is unclear, although the cause may be a viral infection, such as certain strains of the human herpes virus (HHV6 or HHV7).http://www.mayoclinic.com/health/pityria...