Although the cause is unknown, according to the Mayo Clinic, it is believed that pityriasis rosea works by triggering a viral infection that attacks the skin. The result is generally a rash that begins with one large spot on the body followed by many other spots that come to resemble a tree with weeping branches over time. The rash does itch, but it is not contagious.
Most people who get pityriasis rosea are young people between the ages of 10 and 35. Pregnant women are also at risk for getting the condition, and a pregnant woman who gets the rash should see a doctor right away.
A dermatologist can conduct tests to diagnose pityriasis rosea. These might include blood tests or a skin biopsy. Though the rash often goes away by itself within six weeks or less, the patient might still want to see a dermatologist to treat and ease the itching. In such cases, doctors often prescribe an anti-itch medicine. Light therapy can also help with the rash. Self care can include not getting overheated and using only lukewarm water to bathe.
When the rash does improve, it generally does not leave scars. It might leave areas of darker pigmentation, but even these fade over time. Many people who get pityriasis rosea never have another episode.