Causes

As the epidermal layer continually replaces itself, cells are pushed outward where they eventually die and flake off. In most people, these flakes of skin are too small to be visible. However, certain conditions cause cell turnover to be unusually rapid, especially in the scalp. For people with dandruff, skin cells may mature and be shed in 2 - 7 days, as opposed to around a month in people without dandruff. The result is that dead skin cells are shed in large, oily clumps, which appear as white or grayish patches on the scalp skin and clothes.

Dandruff has been shown to be the result of three required factors:^[1]

1. Skin oil commonly referred to as sebum or sebaceous secretions^[2]
2. The metabolic by-products of skin micro-organisms (most specifically Malassezia yeasts)^{[3][4][5][6][7]}
3. Individual susceptibility

Common older literature cites the fungus Malassezia furfur (previously known as Pityrosporum ovale) as the cause of dandruff. While this fungus is found naturally on the skin surface of both healthy people and those with dandruff, it was discovered that a scalp specific fungus, Malassezia globosa, is the responsible agent.^[8] This fungus metabolizes triglycerides present in sebum by the expression of lipase, resulting in a lipid byproduct oleic acid (OA). Penetration by OA of the top layer of the epidermis, the stratum corneum, results in an inflammatory response in susceptible persons which disturbs homeostasis and results in erratic cleavage of stratum corneum cells.^[5]

Rarely, dandruff can be a manifestation of an allergic reaction to chemicals in hair gels/sprays, hair oils, or sometimes even dandruff medications like ketoconazole.

There is no convincing evidence that food (such as sugar or yeast), excessive perspiration, or climate have any role in the pathogenesis of dandruff.