Dandruff is caused by:

• Dry skin – this is the kind you get during the winter when the air is dry
• Irritated, oily skin – sometimes called seborrheic dermatitis
• Sensitivity to a scalp fungus (called Malassezia) can irritate the scalp
• Not shampooing enough – your scalp skin cells die and shed, they can get trapped in oily clumps
• Reaction to certain hair products