Dandruff is an abnormal creation of small scales of dead skin on the scalp. The main causes are a mild form of seborrheic dermatitis or, less frequent, psoriasis on the scalp. The hair on the scalp is usually not affected. Dandruff is a common occurrence and does not pose any health hazard; it is just unobtrusive and can be aesthetic annoyance.
Self-help: wash your hair with a shampoo against dandruff, and stick to the instructions on the bottle. Frequent washing (every two or three days) is usually necessary, at least in the beginning. In some cases, such anti-dandruff shampoo must be used even when the problem is gone to prevent re-creating of the dandruff.
Professional help: if the shampoo does not help, your doctor will probably prescribe a special lotion which contains a corticosteroid drug to preent the main cause of dandruff.
If the scales (of dead skin) are thick and if they stick to the scalp, your doctor may prescribe a lotion containing a slightly acidic substance to remove abnormal skin; this will also contribute to the effectiveness of anti-dandruff shampoo.