What causes oral cancer? Factors that can increase your risk of mouth cancer include: Tobacco use of any kind, including cigarettes, cigars, pipes, chewing tobacco and snuff, among others. Heavy alcohol use. Excessive sun exposure to your lips. A sexually transmitted virus called human papillomavirus (HPV) A weakened immune system. What does cancer in the mouth look like when it starts? In the early stages, mouth cancer rarely causes any pain. Abnormal cell growth usually appears as flat patches. A canker sore looks like an ulcer, usually with a depression in the center. The middle of the canker sore may appear white, gray, or yellow, and the edges are red.