Seborrheic dermatitis is a common condition that usually appears as simple dandruff. It may affect the scalp, the central part of the face and the anterior portion of the chest, as well as flexural creases of the arms, legs and groin. It occurs most often in infants and in adults between 30 and 60 years of age. Patients with acquired immunodeficiency syndrome may have particularly resistant cases of seborrheic dermatitis. Diagnosis of this condition is generally straightforward, but the differential diagnosis includes a variety of conditions, such as psoriasis vulgaris (sebopsoriasis), atopic dermatitis, tinea capitis and candidiasis, as well as other, more rare conditions. Seborrheic dermatitis may be associated with or caused by a variety of underlying disorders. Treatment is generally topical. Steroid creams, selenium, salicylic acid and coal tar preparations, and pyrithione zinc are frequently used to treat this condition.