Pityriasis, or pityriasis rosea, is a skin problem that results in a rash, according to WebMD. The condition generally affects people between the ages of 10 to 35, but it can occur at any age.
Although the specific cause of pityriasis is unknown, it may be caused by a virus, notes WebMD. The condition is not contagious, nor is it caused by an allergic reaction, fungus or bacteria. Symptoms include single, scaly, round or oval pink patches with raised borders; salmon-colored oval patches on the abdomen, chest, back, arms and legs; and mild itching. The condition typically lasts from six to eight weeks, but may linger for up to several months.