"Seborrheic dermatitis is a chronic inflammatory disorder affecting areas of the head and trunk where sebaceous glands are most prominent. Lipophilic yeasts of the Malassezia genus, as well as genetic, environmental and general health factors, contribute to this disorder. Scalp seborrhea varies from mild dandruff to dense, diffuse, adherent scale. Facial and trunk seborrhea is characterized by powdery or greasy scale in skin folds and along hair margins. Treatment options include application of selenium sulfide, pyrithione zinc or ketoconazole-containing shampoos, topical ketoconazole cream or terbinafine solution, topical sodium sulfacetamide and topical corticosteroids."
http://www.aafp.org/afp/2000/0501/p2703.html