Pityriasis rosea is a skin disease marked by patches of pink, oval rash. Although its exact cause is unknown and its onset is not linked to food, medicines or stress, it is thought that this essentially non-contagious condition is set off by a virus. Pityriasis rosea can affect members of either sex of any age. However, it is most common in females and those between the ages of 8 and 35. Symptoms only recur in 3% of the affected.