Seborrheic dermatitis is a papulosquamous disorder patterned on the sebum-rich areas of the scalp, face and trunk. In addition to sebum, this dermatitis is linked to Pityrosporum ovale, immunologic abnormalities and activation of complement.
Severity varies from mild dandruff to exfoliative erythroderma.
Seborrheic dermatitis is associated with normal levels of Pityrosporum ovale, but an abnormal immune response. Seborrheic dermatitis occurs in all races. The condition is slightly worse in males. The usual onset occurs with puberty. It peaks at age 40 and is less severe, but present, in the elderly.