Seborrheic dermatitis is a disease that causes flaking of the skin. It usually affects the scalp. In adolescents and adults, it is commonly called "dandruff." In babies, it is known as "cradle cap." Seborrheic dermatitis can also affect the skin on other parts of the body, such as the face and chest, and the creases of the arms, legs and groin. It usually causes the skin to look a little greasy and scaly or flaky.

Seborrheic dermatitis most often occurs in babies younger than 3 months of age and in adults from 30 to 60 years of age. In adults, it's more common in men than in women.

The exact cause isn't known. The cause may be different in infants and adults. Seborrheic dermatitis may be related to hormones, because the disorder often appears in infancy and disappears before puberty. Or the cause might be a fungus, called malassezia. This organism is normally present on the skin in small numbers, but sometimes its numbers increase, resulting in skin problems.

The treatment of seborrheic dermatitis depends on its location on the body. Treatment also depends on the person's age.