Physicians cannot clearly state the cause of lip and mouth cancers but there are several associated risk factors. These types of cancer appear to be the result of elements that damage the cells in the oral cavity.  The damage may cause the cells to malfunction and rapidly reproduce as cancer cells.

There are several risk factors linked to the growth of cancerous cells in the oral cavity. Tobacco use is the strongest link to lip and mouth cancers. Research has shown that tobacco causes damage to cells in the lining of the mouth, pharynx and larynx. Cells must grow more rapidly to repair this damage. Many of the chemicals found in tobacco cause damage to DNA, which tells the cells how to grow and repair the damage. In essence, tobacco not only damages cells but also inhibits the ability to grow new ones.

The American Cancer Society (ACS) estimates that approximately 90 percent of people with oral or throat cancer use tobacco. The risk of developing these cancers increases with the amount chewed or smoked and the duration of the habit.

Tobacco use includes cigarettes, cigars, pipes and smokeless tobacco (chewing or snuff). Tobacco smoke from cigarettes, cigars and pipe smoking can cause cancers in the mouth or throat, as well as other organs in the body. In addition, pipe smoking can cause a higher number of lip cancers due to the pipestem contact with the lips.

Smokeless or chewing tobacco is particularly harmful to the mouth and is associated with cancers of the cheek, gums and inner surface of the lips. Smokeless tobacco increases the risk of these cancers by 50 times as the harmful components have direct contact with the linings of the mouth. The cancer associated with smokeless tobacco often starts as leukoplakia or erythroplakia, which appear as abnormal white or red patches in the mouth

Secondhand smoke, also known as environmental tobacco smoke (ETS), may contribute to the development of oral cancers. When nonsmokers are exposed to secondhand smoke, they can absorb nicotine and other chemicals similar to the smokers. The greater the exposure to secondhand smoke, the higher the level of compounds in the body.  There are no specific statistics about the risk of oral cancers due to secondhand smoke exposure.

Alcohol use is the second strongest link to oral and throat cancers.  Scientists are unsure if alcohol directly damages the DNA, but research has shown that alcohol increases the penetration of many DNA–damaging chemicals into the cells. This is one reason why tobacco and alcohol use together cause such a large amount of DNA damage.

The ACS estimates that 75 to 80 percent of all patients with oral and oropharyngeal cancer drink excessive amounts of alcohol. These cancers are about 6 times more common in drinkers than nondrinkers.

When alcohol and tobacco use are combined, the risks of developing oral cancer varies according to the:

• Amount and type of tobacco use
• Length of time of smoking or smokeless tobacco
• Amount of alcohol consumption
• Duration of alcohol use
• Combination of smoking and drinking

There are other risk factors for lip and mouth cancers, including:

• Sun exposure. Prolonged exposure to the sun increases the risk of lip cancers, especially on the lower lip. The ACS estimates that more than 30 percent of people with cancers of the lip have occupations associated with significant outdoor exposure.
  
  
• Mouth irritation. Poorly fitting dentures that cause long–term irritation of the lining is thought to be a risk factor for oral cancer. Poorly fitting dentures may allow causative cancer agents, such as alcohol and tobacco particles, to be trapped under them. Research studies, however, have not shown an increase in oral cancers between denture wearers and non-denture wearers. In addition, some studies have found individuals, particularly men, with chronic gum may have a higher risk of tongue cancer.
  
  
• Poor nutrition. A diet low in fruits and vegetables may increase the risk of developing cancer in the oral cavity and oropharynx. Without fruits and vegetables, the cells are deprived of the nutrients that help keep them healthy.
  
  
• Human papillomavirus (HPV) infection. Papillomaviruses are a large group of related viruses, some of which have a role in causing cancer. One type of HPV is thought to be linked to oral cancers in about 20 percent of the people. People with HPV are less likely to be smokers and drinkers and have a better prognosis for recovery from oral cancer, according to the ACS.
  
  
• Immune system suppression. For reasons that are not clear, individuals who are taking immunosuppressive drugs are more at risk for oral and oropharyngeal cancers. These drugs are taken to treat immune system diseases or to prevent the rejection of a transplanted organ.
  
  
• Industrial exposures. Inhalation of industrial elements, such as wood and nickel dust, may contribute to the development oral cancers. Although exposure is mostly linked to cancer of the nose and throat, some oral cancers may result from these elements.
  
  
• Radiation. Radiation to the head and neck can increase the risk of oral and throat cancer, particularly for the salivary glands. The radiation exposure can come from diagnostic x-rays or radiation therapy for medical conditions.