Jan McCoy, age 9, of Springfield, Mass., for her question:

WHAT EXACTLY IS DANDRUFF?

Dandruff is made up of flakes of skin thrown off by the scalp. The flakes are mixed with grease that comes from the scalp's oil glands. Some scaling of the skin of the scalp is completely normal. But when the scalp loses many scales, the product is called dandruff. Some dandruff can be prevented by proper washing, brushing and occasional oiling of the scalp and hair.

Dandruff definitely does not cause baldness.

The condition called seborrhea sometimes causes dandruff. Many authorities consider seborrhea a mild bacterial disease. In seborrhea, the scalp is red and itchy, and the dandruff is more greasy than usual.

Keeping the head clean helps prevent seborrhea. See a doctor if you need treatment.