Craig Carrier, age 14, of Willingboro, N.J., for his question:

WHAT CAUSES DANDRUFF?

Dandruff is a condition in which the skin of the scalp flakes off in excessive amounts. Dandruff may be due to dry scalp or excess secretion from the sebaceous glands, but the cause of the condition is unknown.

Depending on the severity of the dandruff, treatment may include frequent shampooing or use of a shampoo prescribed by a doctor.

Simple dandruff is noninflammatory, but a more serious condition called seborrheic dermatitis is characterized by scaling and redness, not only in the scalp but also in the eyebrows, the creases behind the ears and on each side of the nose. In severe cases, red patches may also occur in the armpits and groin.

Seborrheic dermatitis is a chronic condition that can be controlled but not cured. The first item of therapy is often the use of a special shampoo designed to slow down the production of scales and wash away those already formed.

Tar based shampoos are sometimes recommended. Some doctors also use a steroid spray.