Oral or mouth cancer most commonly involves the tissue of the lips or the tongue. It may also occur on the floor of the mouth, cheek lining, gingiva (gums), or palate (roof of the mouth). Most oral cancers look very similar under the microscope and are called squamous cell carcinomas. These are malignant and tend to spread rapidly.

The exact cause is unknown. Smoking and other tobacco use are associated with 70-80% of oral cancer cases. Smoke and heat from cigarettes, cigars, and pipes irritate the mucous membranes of the mouth. Use of chewing tobacco or snuff causes irritation from direct contact with the mucous membranes. Heavy alcohol use is another high-risk activity associated with oral cancer.

Other risks include poor dental and oral hygiene and chronic irritation (such as that from rough teeth, dentures, or fillings). Some oral cancers begin as leukoplakia or mouth ulcers. Oral cancer accounts for about 8% of all malignant growths. Men are affected twice as often as women, particularly men older than 40.