The medical name for this condition is Pityriasis capitis . Many people think that flaking occurs because their scalp is too dry, and stop using shampoo because they believe it makes the condition worse. This is not true. Very severe cases of dandruff are caused by a disease called seborrhoeic eczema or seborrhoeic dermatitis. This can vary from mild cases, which are only a problem in winter, to more severe cases where flaking occurs in places other than just the scalp.
Seborrhoeic dermatitis causes greasy, bran-like scale.
The problem becomes worse during the winter and tends to improve during the summer when sunlight relieves the symptoms. A fungus called Pityrosporum Ovale is a significant factor in this condition. Doctors don't know exactly why, but anti-fungal treatment helps deal with the problem. As well as seasonal changes, stress and serious illnesses can cause an increase in the production of scale. A sudden, strong tendency to flaking or seborrhoeic dermatitis in a middle-aged person who has never had any such problems before can be a sign of HIV infection.