Definition of Pityriasis rosea:

Pityriasis rosea is a common type of skin rash seen in young adults.

Causes, incidence, and risk factors:

Pityriasis rosea is believed to be caused by a virus. It occurs most often in the fall and spring. Although pityriasis rosea may occur in more than one person in a household at a time, it is not thought to be highly contagious.

Attacks generally last 4 - 8 weeks. Symptoms may disappear by 3 weeks or last as long as 12 weeks. There is generally a single large patch (herald patch) followed several days later by a rash.