Pityriasis rosea is a type of skin rash. Classically, it begins with a single red and slightly scaly area known as a "herald patch". This is then followed, days to weeks later, by an eruption of many smaller scaly spots; pinkish with a red edge in people with light skin and greyish in darker skin. About 20% of cases show atypical deviations from this pattern. It usually lasts less than three months and goes away without treatment. Sometimes malaise or a fever may occur before the start of the rash or itchiness, but often there are few other symptoms. While the cause is not entirely clear, it is believed to be related to human herpesvirus 6 (HHV6) or human herpesvirus 7 (HHV7). It does not appear to be contagious. Certain medications may result in a similar rash. Diagnosis is based on the symptoms. Evidence for specific treatment is limited. About 1.3% of people are affected at some point in time. It most often occurs in those between the ages of 10 and 35. The condition was described at least as early as 1798. Signs and symptoms The symptoms of this condition include: Recent upper respiratory tract infections in 8–69% of patients have been reported by some studies. Occasionally, prodromal flu-like symptoms, including headache, joint pain, mild fever, and fatigue, as well as gastrointestinal symptoms such as nausea, diarrhea, or vomiting, and feeling generally unwell, precede other symptoms. In most cases, a single, 2 to 10 cm (1" to 4") oval red "herald" patch appears, classically on the trunk or neck, having an appearance similar to ringworm. Occasionally, the herald patch may occur in a hidden position (in the armpit, for example) and not be noticed immediately. The herald patch may also appear as a cluster of smaller oval spots, and be mistaken for acne. Rarely, it does not become present at all. After the herald patch appears, usually some days or weeks later, a rash of many small (5–10 mm; " to ") pink or red, flaky, oval or round spots appear. They are mostly situated on the trunk and upper limbs. They follow the skin's cleavage lines, which on the upper chest and back produce a characteristic "christmas-tree" distribution. In 6% of cases an "inverse" distribution may occur, with rash mostly on the extremities. In children, presentation can be atypical or inverse, and the course is typically milder. About