Scalp itchiness is a problem afflicting 43 percent of the general population at least once in a 12-month period. Many factors contribute to this including blow-dryers, styling products, wool hats, allergies, dandruff, mites, and even stress. The scalp can reflect the overall condition of the body and is affected by stress and hormonal changes. A overstressed immune system lowers resistance, which can result in over-colonization of a yeast organism called Pityrosporum ovale. Although it's a normal part of the human skin flora, an overpopulation of this fungus can cause dermatitis and dandruff.