Seborrheic dermatitis.

Seborrheic dermatitis is a common chronic inflammatory skin condition, characterized by scaling and poorly defined erythematous patches. It may be associated with pruritus, and it primarily affects sebum-rich areas, such as the scalp, face, upper chest, and back. Although its pathogenesis is not completely understood, some postulate that the condition results from colonization of the skin of affected individuals with species of the genus Malassezia (formerly, Pityrosporum). A variety of treatment modalities are available, including eradication of the fungus, reducing or treating the inflammatory process, and decreasing sebum production.