**4. Etiology of oral cancer**

Numerous studies have demonstrated a multifactoral etiology in the development and carcinogenesis of oral cancer, involving tobacco, alcohol, betel quid, high-risk human papillomavirus (HPV) 16/18, poor nutrition, poor oral hygiene, immune system suppression, bacterial infection, and so on.

#### **4.1 Tobacco**

Tobacco is a well-established risk factor for lots of cancers as well as oral cancer. There are more than 80% of oral cancer patients with a habit of tobacco use. All types of tobacco products, for example cigarettes, pipe tobacco, chewing tobacco, contain many carcinogenic molecules, especially nitrosamines, benzopyrenes and polycyclic hydrocarbons, raising the risk of generating cancers. For tobacco smoking, it has a combined odds ratio of 4.65 (95% CI, 3.19–6.77) related with oral cancer [14]. For smokeless tobacco such as paan chewing and gutkha swallowing, it would lead to oral submucous fibrosis (OSMF) and ultimately increase the potential to transform into oral cancer. According to a nested case–control study in India, tobacco chewing was found the most potent high-risk factor linked to oral cancer, with adjusted odds ratios (ORs) of 3.1 for males and 11.0 for females [15].

#### **4.2 Alcohol**

Alcohol is also a well-defined significant risk factor for oral cancer [16–18]. An updated analysis based on cohort and case–control studies from 1988 to 2009

#### *Oral Cancer DOI: http://dx.doi.org/10.5772/intechopen.97330*

shows that, a consumption of 60 g per day or more than 4 drinks per day would raise the risk of oral cancer by 3–9 times when adjusted for smoking and other potential confounding variables [19]. The risk between alcohol and oral cancer is not only dose–response, but also related with the type of alcoholic beverage, meaning those consuming hard liquor or beer have a higher risk than those consuming wine. Besides, a greater significance is observed in both heavy smoker and heavy drinker [18].
