Chewing betel nuts, followed by smoking, is the primary cause of mouth cancer in India.

There is a clear link between tobacco use and the development of oral cavity malignancies. Almost all oral cancer patients have smoked at some point in their lives. Tobacco smokers are 25 times more likely than non-users to acquire oral cancer. Quitting smoking lowers the risk of mouth cancer substantially. If a person quits smoking for more than nine years at a time, his or her risk drops by around half.

Reverse smoking raises the chance of hard palate cancer.

Reverse smoking is a smoking behaviour in which the unlit/filtered end of a hand-rolled tobacco leaf is chewed rather than the burnt or burning end. This is a popular practice in Andhra Pradesh (India), and the Philippines.