It's a natural condition, yet dandruff is still a cause of embarrassment to the many people who suffer its scattering of white flakes across the collar. The exact cause of the condition is a yeast called Malassezia globosa, that feeds off natural oils in human skin. This releases a toxin that can cause irritation, leading to the itchiness and flaking associated with dandruff.
Cleanliness is important in keeping dandruff under control. It's thought to be more of a problem with dry scalps, but oily scalps actually bind the flakes together more noticeably. Either way, washing regularly will add moisture to skin and break down oiliness. Medicated shampoos also help by killing off fungal infections.