Dandruff (also called scurfand historically termed Pityriasiscapitis) is the shedding of dead skin cells from the scalp. Dandruff issometimes caused by frequent exposure to extreme heat and cold. As it is normalfor skin cells to die and flake off, a small amount offlaking is normal and common. Some people, however, either chronically or as a result of certain triggers, experience an unusually largeamount of flaking, which can also be accompanied by redness and irritation.Most cases of dandruff can be easily treated with specialized shampoos.
Excessive flaking can also be a symptom of seborrhoeic dermatitis, psoriasis, fungal infectionor excoriation associated with infestation of head lice.
Those affected by dandruff find that it can cause social or self-esteemproblems. Treatment may be important for both physiological and psychologicalreasons.
As the epidermallayer continually replaces itself, cells are pushed outward where theyeventually die and flake off. In most people, these flakes of skin are toosmall to be visible. However, certain conditions cause cell turnover to beunusually rapid, especially in the scalp. For people with dandruff, skin cellsmay mature and be shed in 2–7 days, as opposed to around a month in peoplewithout dandruff. The result is that dead skin cells are shed in large, oilyclumps, which appear as white or grayish patches on the scalp, skin andclothes.
Dandruff has been shown to be the result of three required factors:
- Skin oil commonly referred to as sebum or sebaceous secretions
- The metabolic by-products of skin micro-organisms (most specifically Malassezia yeasts)
- Individual susceptibility
Common older literature cites the fungus Malasseziafurfur (previously known as Pityrosporumovale) as the cause of dandruff. While this fungus is found naturally onthe skin surface of both healthy people and those with dandruff, it was laterdiscovered that a scalp specific fungus, Malasseziaglobosa, is the responsible agent. This fungus metabolizes triglyceridespresent 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 stratumcorneum, results in an inflammatory response in susceptible persons whichdisturbs homeostasisand results in erratic cleavage of stratum corneum cells.
Rarely, dandruff can be a manifestation of an allergic reaction tochemicals in hair gels/sprays/shampoos, hair oils, or sometimes even dandruffmedications like ketoconazole.
There is some evidence that food (especially sugar and yeast), excessive perspiration,and climate have significant roles in the pathogenesis of dandruff.