The cause of pityriasis rubra pilaris is unknown.
The two most common forms of the disorder are
The juvenile classic form of pityriasis rubra pilaris is inherited and begins in childhood. The adult classic form of pityriasis rubra pilaris does not seem to be inherited and begins in adulthood.
Other nonclassic forms exist in both age groups. Sunlight, human immunodeficiency virus (HIV) infection or another infection, minor trauma, or an autoimmune disorder may trigger a flare-up.
Doctors base the diagnosis of pityriasis rubra pilaris on how the scales and plaques look and where they appear on the body.
Treatment of pityriasis rubra pilaris is very difficult. Symptoms of the disorder may be lessened, but the disorder itself can almost never cured. Classic forms of the disorder go away slowly over 3 years, whereas nonclassic forms last much longer.
To reduce scaling, doctors may give skin moisturizers (emollients) or have people apply lactic acid under a dressing that keeps air away from the skin (occlusive dressing), followed by corticosteroids applied to the skin. Vitamin A taken by mouth may be effective. Acitretin or methotrexate taken by mouth is an option when treatments applied to the skin are not helping.