What is Dandruff?

Dandruff is believed to be related to a fungus known as Malassezia (formerly termed pityrosporum) that lives on the scalp of most people. In some cases, overgrowth of the fungus results in the flakiness of the skin characteristic of dandruff. The reasons for the overgrowth of fungus are unclear but may be related to increased oil production, hormonal changes, stress, neurologic disorders such as Parkinson’s disease, recovery from chronic conditions such as stroke or heart attack, suppression of the immune system, and infrequent shampooing.

Dandruff itself produces no symptoms. However, the most common cause of dandruff, seborrheic dermatitis (seborrhea), is an itchy red rash that tends to occur on the scalp, ears, face, mid-chest, and mid-back. The cause of seborrhea is unknown, although a yeast that often lives on the skin, Malassezia furfur, may play a role.

Scalp seborrhea may slow hair growth but does not cause permanent hair loss.

Often, scalp seborrhea doesn’t even itch significantly. Seborrhea can appear during infancy, starting shortly after birth and lasting several months. It may affect the scalp (“cradle cap”) or produce scaly plaques on the body. Seborrhea may occur at any age.

Some people who have weakened immune systems, such as those on chemotherapy or those with HIV disease or certain neurological disorders, may have very severe seborrhea. It is important to emphasize, however, that seborrhea is a very common condition, affecting perhaps 5% of the population (with men predominating). The vast majority of those who have it are completely healthy and have no internal or immune problems.

There are a variety of other inflammatory diseases that can produce excessive scaling and therefore dandruff, including psoriasis, fungal infection of the scalp skin (tinea capitis), and allergic contact dermatitis.