Pityriasis rosea is an acute, self-limiting skin disease, probably infective in origin, affecting mainly children and young adults, and characterised by a distinctive skin eruption and minimal constitutional symptoms. The cause of pityriasis rosea is uncertain, but many epidemiological and clinical features suggest that an infective agent may be implicated. In the majority of cases the disease follows a characteristic course whereby a so-called herald patch, larger than subsequent lesions, appears several days before the eruption of multiple oval scaly pink macules over the trunk and proximal limbs predominantly.