The major risk factors for oral cancer include tobacco use, alcohol consumption, HPV infection, and prolonged sun exposure.

1. Tobacco Use:

• Smoking tobacco, chewing tobacco, or using smokeless tobacco (like snuff and betel quid) significantly increases the risk of oral cancer.
  
• The risk increases with the amount and duration of tobacco use.
  
• Smoking and chewing tobacco together increase the risk even more.
  

2. Alcohol Consumption:

• Excessive alcohol consumption is a well-established risk factor for oral cancer.
• Combining alcohol with tobacco use further increases the risk.
  

3. Human Papillomavirus (HPV) Infection:

• Some HPV strains, particularly HPV-16, have been linked to oral cancers, especially oropharyngeal cancer.
  
• While HPV is primarily a sexually transmitted infection, it can also cause oral cancer.
  

4. Sun Exposure:

• Prolonged exposure to ultraviolet (UV) light from the sun or tanning beds can increase the risk of lip cancer. 

5. Other Risk Factors:

• Poor diet: A diet low in fruits and vegetables may increase the risk.
  
• Weakened immune system: Conditions like HIV/AIDS or immunosuppressant medications can increase the risk of oral cancer.
  
• Genetic factors: Some people have a genetic predisposition to oral cancer.
  
• Age: The risk of oral cancer increases with age, particularly after 45.
  
• Sex: Men are more likely to develop oral cancer than women. 

6. Precancerous Conditions:

• Leukoplakia and erythroplakia are precancerous conditions that can sometimes develop into oral cancer if not treated.