Causes of mouth cancer

Cancer begins with a change in the structure of DNA. DNA provides our cells with a basic set of instructions, such as when to grow and reproduce.

A change in DNA structure is known as a mutation, and it can alter the instructions that control cell growth. This means that cells continue to grow instead of stopping when they should. This causes the cells to reproduce in an uncontrollable manner, producing a lump of tissue called a tumour.

How mouth cancer spreads

There are two ways mouth cancer can spread:

• directly – the cancer can spread out of the mouth and into nearby tissues, such as surrounding skin or into the back of the jaw
• via the lymphatic system – the lymphatic system is a series of glands (or nodes) located throughout your body (similar to the blood circulatory system), glands produce many specialised cells needed by your immune system to fight infection

Mouth cancer that spreads to another part of the body is known as metastatic oral cancer.

Risk factors

Exactly what triggers the changes in DNA that lead to mouth cancer and why only a small number of people develop mouth cancer is still uncertain.

However known risk factors include:

Smoking and alcohol

The two leading causes of mouth cancer are smoking cigarettes (or other tobacco products, such as pipes or cigars) and drinking too much alcohol. Both of these substances are carcinogenic, which means they contain chemicals that can damage the DNA in cells and lead to cancer.

The risk of mouth cancer increases significantly in somebody who is both a heavy smoker and heavy drinker.

For example, research has shown that if you smoke 40 cigarettes a day, but do not drink alcohol, you are five times more likely to develop mouth cancer than someone who does not drink or smoke.

If you do not smoke, but drink an average of 30 pints a week, your risk also increases by a factor of five.

However, if you smoke more than 40 cigarettes a day and you drink an average of 30 pints a week, you are 38 times more likely to develop mouth cancer.

Betel nuts

Betel nuts are mildly addictive seeds taken from the betel palm tree, and are widely used in many southeast Asian ethnic communities, such as people of Indian and Sri Lankan origin.

They have a stimulant effect similar to coffee. Betel nuts also have a carcinogenic effect, which can increase the risk of mouth cancer. This risk is made worse as many people enjoy chewing betel nuts along with tobacco.

Due to the tradition of using betel nuts, rates of mouth cancer are much higher in ethnic Indian and Sri Lankan communities than in the population at large.

Read more about south Asian health issues.

Smokeless tobacco

Smokeless tobacco is a general term used to refer to a range of products, such as:

• chewing tobacco
• snuff – powdered tobacco designed to be snorted
• snus – a type of smokeless tobacco popular in Sweden, which is placed under your upper lip, where it is gradually absorbed into your blood

Smokeless tobacco products have become increasingly popular in England, most likely as a result of the 2007 smoking ban.

Smokeless tobacco products are not harmless, as many people mistakenly assume, and many increase your risk of developing mouth cancer, as well as other cancers, such as liver cancer, pancreatic cancer and oesophageal cancer.

Cannabis

Smoking cannabis has also been linked to an increased risk of mouth cancer. Regular cannabis smokers may have a higher risk than tobacco smokers because cannabis smoke contains higher levels of tar than tobacco smoke, and tar is carcinogenic.

Human papilloma virus (HPV)

The human papilloma virus (HPV) is the name of a family of viruses that affect the skin and moist membranes that line your body, such as those in your cervix, anus, mouth and throat.

You can contract a HPV infection by having sexual contact with a person already infected – you do not have to have ‘full sex’; just close skin-to-skin contact.

Infection with some types of HPV can cause abnormal tissue growth and other changes to the cells, which can lead to the development of cervical cancer.

There is evidence that some types of HPV infection could also cause abnormal tissue growth inside the mouth, triggering some cases of mouth cancer.

It is thought HPV infection is the probable cause of mouth cancer in young people who have few or none of the expected risk factors.

Diet

There is evidence that a diet high in red meat, processed food and fried food can increase your risk of developing mouth cancer.

Poor oral hygiene

There is evidence that poor oral hygiene, such as having tooth decay, gum disease, not brushing your teeth regularly and having ill-fitted dentures (false teeth) can increase your risk of mouth cancer.

Qat

Qat is a green-leafed plant found in Africa and southern Arabia. There is a long tradition in many countries of chewing qat as it has a mild stimulant effect.

In England, the use of qat is usually limited to people of Somalian, Ethiopian and Yemeni origin.

There is some limited evidence that qat may increase the risk of mouth cancer, but because many people chew qat with tobacco, it is hard to estimate the independent risk factor of qat.