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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. Seborrheic dermatitis 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 Pityrosporum ovale. This organism is normally present on the skin in small numbers, but sometimes its numbers increase, resulting in skin problems.

Seborrheic dermatitis has also been linked to neurologic disorders such as Parkinson's disease and epilepsy. The reason for this relationship isn't known.

Seborrheic dermatitis of the scalp (dandruff) in adults and adolescents. Dandruff is usually treated with a shampoo that contains salicylic acid (some brand names: X-Seb, Scalpicin), the prescription medicine selenium sulfide (brand names: Selsun, Exsel) or pyrithione zinc (some brand names: DHS Zinc, Head & Shoulders). These shampoos can be used 2 times a week. Shampoos with coal tar (some brand names: DHS Tar, Neutrogena T/Gel, Polytar) may be used 3 times a week. If you have dandruff, you might start by using one of these shampoos daily until your dandruff is controlled, and then use it 2 or 3 times a week.

When you use a dandruff shampoo, rub the shampoo into your hair thoroughly and let it stay on your hair and scalp for at least 5 minutes before rinsing. This will give it time to work.

If the shampoo alone doesn't help, your doctor might want you to use a prescription steroid lotion once or twice daily, in addition to the shampoo.

Seborrheic dermatitis of the scalp (cradle cap) in babies. Seborrheic dermatitis of the scalp in babies is treated with products that are not as strong as those used in adults. You might start with a mild, nonmedicated baby shampoo. Brushing your baby's scalp with a soft brush, like a toothbrush, can help loosen scales or flakes. But be gentle when massaging or brushing your baby's scalp--a break in the skin makes it vulnerable to infection. If a nonmedicated shampoo doesn't work, talk to your doctor about switching to a shampoo that contains tar. Or your doctor may recommend a prescription shampoo that contains 2% ketoconazole (brand name: Nizoral).

Seborrheic dermatitis of the skin creases in babies. Gentle steroid lotions or creams may be used to treat seborrheic dermatitis in the skin creases of babies.