Pityriasis rosea is a viral rash lasting about 6-12 weeks. It can sometimes follow a few days after an upper respiratory tract viral infection. It most often affects teenagers and young adults; however it can affect males and females of any age.
Pityriasis rosea is associated with reactivation of viruses mainly herpesviruses 6 and 7. Other triggers such as Influenza viruses and vaccines have been described.
The rash is characterised by a herald patch followed by similar, smaller oval red patches that are located mainly on the chest and back. The herald patch is a single plaque that appears 1–20 days before the generalized rash of pityriasis rosea. It is an oval pink or red plaque 2–5 cm in diameter, with a scale around it.
A few days after the appearance of the herald patch, more scaly lesions or plaques appear on the chest and back. These plaques are generally uncommon on the face or scalp. These secondary lesions tend to be smaller than the herald patch.
Pityriasis rosea plaques usually follow cleavage lines of the neck, chest and upper abdomen. The appearance of the rash is often described as a fir tree-like . It usually does not affect the face or scalp
The diagnosis of pityriasis rosea is usually made clinically but may be supported by the finding of subacute dermatitis on histopathology of a skin biopsy.
The treatment of pityriasis rosea is usually supportive advising to bathe or shower with plain water and bath oil, aqueous cream, or another soap substitute, to apply moisturising creams to dry skin and expose skin to sunlight cautiously (without burning). In persistent cases phototherapy with UVB light may be considered.