Dandruff Causes and Severity
Dandruff (pityriasis capitis) occurs when the scalp sheds larger than normal amounts of dead epidermal cells. It is sometimes associated with seborrhea where sebum production is excessive. Dandruff shares some features with seborrheic dermatitis, and both conditions are frequently treated with common topical medications. Seborrheic dermatitis generally affects body sites in addition to the scalp, including the forehead, nasolabial fold, eyelash and eyebrow regions, and the outer ear.
The peak incidence and severity of dandruff occurs at approximately 20 years of age. Dandruff appears on the scalp as small white or gray scales. In the presence of seborrhea, the scales may appear greasy and yellow in color. The greasy scales combine with exudates to form crusts, beneath which the scalp is red and moist. Shampooing removes the scales temporarily, however they return within several days.
Dandruff is associated with fewer cell layers in the outer most portion of the epidermis, however the cells are often irregular and display a rapid turnover rate. The reason for the rapid turnover is uncertain. For many years dandruff has been associated with the presence of yeast/fungi of the genus Malassezia or Pityrosporum. At this time, the species Pityrosporum ovale is considered the main causative agent, although some investigators argue that the altered flora of the scalp is secondary to increased epidermal proliferation. Seborrheic dermatitis has also been associated with the activities of Pityrosporum fungi. Effective therapies of both dandruff and seborrheic dermatitis have been linked to agents that inhibit these organisms.