Psoriasis is a common, chronic skin disorder.
It begins in childhood or adolescence for perhaps one third of all affected persons. About half of all children with psoriasis have a family history of the disease. Girls are more frequently affected in childhood. The rash of psoriasis consists of reddish papules that coalesce to form raised plaques with sharply defined, irregular borders. A characteristic thick, silvery or yellow-white scale develops in untreated psoriasis.