The skin of the scalp usually sheds dead cells gradually, which is not a noticeable process. In the case of dandruff, however, this shedding is accelerated and leads to visible deposits of dead skin in the hair.

The epidermal layer is constantly regenerating itself, with cells being pushed outwards, dying and flaking. These flakes of skin are usually too small to be noticeable but in some conditions, cell turnover is very fast and it is thought that in the case of dandruff, it may only take 2 to 7 days for skin cells to mature and be shed, as opposed to the usual period of a month or so. This leads to the formation of clumps of dead skin cells that may be visible on the scalp and skin.

One study into dandruff suggested that the condition may occur due to three factors:

• Secretions of oil from the skin, also called sebaceous secretions
• The presence of a yeast in the skin called Malassezia that triggers inflammatory reactions  
• Genetic tendency to develop dandruff

The Malassezia fungi are normally present on the scalp, but in 2007, one study showed that a specific species called Malassezia globosa uses lipase to break down triglycerides present in skin oil, which produces oleic acid. This acid penetrates the top layer of the epidermis and triggers an inflammatory response.

Some factors that are known to worsen dandruff include:

• Emotional stress
• The use of some hair products such as hair gel and hairspray
• Both too much and too little hair washing can aggravate dandruff
• Concomitant skin conditions such as eczema or psoriasis can make dandruff worse
• Individuals with a weak or deficient immune system may be more susceptible to dandruff