Pityriasis rosea is an acute, self-limiting skin eruption with a distinctive and constant course, with an initial lesion that is a primary plaque that is followed after 1 or 2 weeks by a generalized secondary rash with a typical distribution and lasting for about 6 weeks. The specific cause of the disorder remains unclear; however, strong evidence suggests that it is due to a reactivation of latent human herpes virus-6 (HHV-6) and human herpes virus-7 (HHV-7) infection.

A herald patch is a pink macule or papule that gradually expands over a few days to become a 2- to 10-cm, salmon-pink–to–brown, oval plaque. The lesion is scaly and may exhibit central clearing, which mimics tinea corporis (yeast skin infection). A single, large red "herald" patch may occur 1 to 20 days before smaller, more numerous patches of rash. A primary herald patch is most commonly observed on the trunk, neck, and proximal extremities. 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. Approximately 50-80% of patients present with a herald patch.

Skin lesions similar to those in Pityriasis rosea can be also found in: Pityriasis Alba, Syphilis, Drug eruptions, Guttate psoriasis, Lichen planus, Nummular eczema, Pityriasis lichenoides, Tinea corporis, Viral exanthems.

There are no clinical data that Pityriasis rosea gets worse during the evening.