Dandruff is small white pieces of dead skin in someone's hair, or fallen from someone's hair. He has very bad dandruff. small pieces of dead skin from someone's head that can be seen in their hair or on their shoulders. Skin disorder of the scalp, a mild form of dermatitis. It affects most people at some time, when the scalp, which normally sheds its dead outer skin cells continuously, starts to shed them intermittently, causing a scaly buildup before shedding and noticeable flakes of skin when shedding occurs. Dandruff is not contagious and often goes away spontaneously; special shampoos can control it