The oral mucosa is lined by stratified squamous epithelium and has topographic differences that correlate with physical demands or a higher degree of specialization. For example, the epithelium lining the floor of the mouth, the ventral side of the tongue, the buccal mucosa, and the soft palate is nonkeratinized; however, the epithelium associated with the gingiva and hard palate is usually keratinized. The dorsal surface of the tongue is also keratinized, but it is referred to as specialized mucosa because of the presence of papillae. The dorsum of the tongue, the hard palate, and the gingival tissues are keratinized to better respond to masticatory demands.

Hyperkeratinization (excessive formation of tenaciously attached keratin) may be present in a variety of clinical conditions, including genetic, physiologic, inflammatory, immunologic, premalignant, and malignant conditions. The change may result from a local insult, including chemical, thermal, or physical irritants. This article focuses on the oral hyperkeratinization that results from friction. Friction (the constant rubbing of 2 surfaces against one another) in the oral cavity may result in the development of clinically observable white patches.

Various names have been used to describe particular examples of frictional keratosis (FK). These include frictional keratosis arising from excessive force while brushing the teeth (toothbrush keratosis); the constant rubbing of the tongue against the teeth (tongue thrust keratosis); the constant sucking, pressure, and irritation of the teeth against the buccal mucosa along the plane of occlusion (linea alba); and the habit of chronic cheek, tongue, or lip biting (cheek- or lip-bite keratosis). [1] Injuries to the oral mucosa, using items such as a pen, toothpicks, or fingernails, may result in frictional keratosis.