Dandruff is the shedding of the skin on the scalp that leads to white flakes on the head, neck and shoulders. If the dandruff flakes are greasy and yellow in colour, and the underlying scalp is red, you probably have the skin condition seborrhoeic dermatitis.

Large silvery scales are relatively rare and may be an indication of psoriasis of the scalp. Although most doctors are aware that dandruff is the result of skin cells that grow and die too quickly, the reason for this is still not known.

For some people, sensitivity to certain hair products can trigger dandruff. It may also be caused by a fungus, Malassezia. Other potential triggers for dandruff include changes in hormones, stress, illness and too much oil on your scalp.