389 Chapter 12 Dandruff and Seborrheic Dermatitis: A Head Scratcher James R. Schwartz, Yvonne M. DeAngelis, and Thomas L. Dawson, Jr. Introduction The visual perception of individually distinguishable flakes on the scalp, in the hair, or on the clothing is considered an abnormal condition frequently referred to as dandruff, seborrheic dermatitis, or multiple other names.1-2 This condition is, however, most often referred to as dandruff, especially in the public domain of non- technical literature and advertising. In the medical literature, the same disorder, though often in a more severe form, is most commonly referred to as seborrheic dermatitis. Historically, there have been multiple other descriptive names reflecting the fungal cause of this condition, such as pityriasis simplex and pityriasis capitis (referring to Pityrosporum) and furfuracea (referring to Malassezia furfur). As all of these names remain in use, we simply need to remember they represent a continuum of the same symptoms based on the same causes and with similar treatment.1,3 More than 50% of adults may be affected by these conditions, which suggests a high socioeconomic impact. For dandruff and seborrheic dermatitis alone, the health care direct, indirect, and intangible costs exceeded $1.4 billion in the United States in 2004.4 Study of dandruff and seborrheic dermatitis is more important than is often perceived, as its presence is now documented to lead to significant psychological trauma, manifesting in the loss of self-esteem and the