Dandruff is a harmless, chronic condition that occurs when the scalp becomes dry or greasy and produces white flakes of dead skin that appear in the hair or on the shoulders. People most often think of dandruff as anything that produces a flaky scalp.
Although it is harmless, dandruff can be embarrassing for those who have it. Dandruff usually starts between the ages of 10 and 20 and affects up to 40% of people over the age of 30.
Skin cells are formed continuously on the scalp, so the shedding of dead skin cells is a normal process. With dandruff, however, skin cells are shed at a faster rate than normal. Oil from the scalp causes the skin cells to clump together and appear as white flakes.
Dandruff can be caused by a number of things, including dry skin; sensitivity to hair products; and skin conditions such as psoriasis, seborrheic dermatitis, or eczema.
The overgrowth of yeast can also cause dandruff. This overgrowth can be caused by stress, hormones, too much oil on the scalp, or problems with the immune system.
The symptoms of dandruff include white flakes of dead skin in the hair and on the shoulders, as well as an itchy, red, or scaly scalp. Common dandruff flakes are usually scattered throughout the scalp.
If seborrheic dermatitis is the cause of dandruff, the symptoms usually appear gradually. The scalp becomes dry or greasy and feels itchy. As skin cells die, they turn to yellowish scales. A bad case of seborrheic dermatitis can also cause symptoms in other parts of the body. Yellowish or reddish scaling can appear on the hairline, in and around the ears, or on the nose and chest. Affected newborn babies may get a thick and crusty rash on the scalp, called cradle cap.
The flakes associated with psoriasis look like silver scales, which may also commonly be apparent on the ears, extremities, trunk, palms, and soles.