Dandruff is a common scalp disorder affecting almost half of the population at the pre-pubertal age and of any gender and ethnicity. The word dandruff is of Anglo-Saxon origin. As the outer layer of skin 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. The result is that dead skin cells are shed in large, oily clumps, which appear as white or greyish patches on the scalp, skin and clothes. 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.
Dandruff is mostly caused by frequent exposure of skin to extreme heat and cold. Rarely, dandruff can be a manifestation of an allergic reaction to chemicals in hair gels, sprays, and shampoos, hair oils, or sometimes even dandruff medications like ketoconazole. There is some evidence that excessive perspiration and climate have significant roles in causing dandruff. The severity of dandruff may fluctuate with season as it often worsens in winter. Those affected by dandruff find that it can cause social or self-esteem problems. Treatment may be important for both physiological and psychological reasons. Most cases of dandruff can be easily treated with specialised shampoos.