Seborrheic dermatitis (SD) is inflammation of skin regions with
a high density of sebaceous glands (eg, face, scalp, upper
trunk). The cause is unknown, but Malassezia (formerly
Pityrosporum) ovale, a normal skin organism, plays some role. SD
occurs with increased frequency in patients with HIV and in
those with certain neurologic disorders. SD causes occasional
pruritus, dandruff, and yellow, greasy scaling along the
hairline and on the face. Diagnosis is made by examination.
Treatment is tar or other medicated shampoo and topical
corticosteroids and antifungals. Despite the name, the
composition and flow of sebum are usually normal. The
pathogenesis of SD is unclear, but its activity has been linked
to the number of Malassezia yeasts present on the skin. The
incidence and severity of disease seem to be affected by genetic
factors, emotional or physical stress, and climate (usually
worse in cold weather). SD may precede or be associated with
psoriasis (called seborrhiasis). SD may be more common and more
sev