The two leading causes of mouth cancer in the UK are tobacco and alcohol.
Both tobacco and alcohol 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 people who smoke and drink heavily.
Some people also chew tobacco or other substances that are carcinogenic.
It's not known exactly what triggers the DNA changes that lead to mouth cancer and why only a small number of people develop it.
Other risk factors
Other risk factors for mouth cancer may include:
- chewing tobacco or other smokeless tobacco products
- chewing betel nuts with or without tobacco
- a poor diet
- the human papilloma virus (HPV)
Smokeless tobacco products include:
- chewing tobacco
- snuff – powdered tobacco designed to be snorted
Smokeless tobacco products aren't harmless and may increase your risk of developing mouth cancer, as well as other cancers, such as liver cancer, pancreatic cancer and oesophageal cancer.
Betel nuts are mildly addictive seeds from the betel palm tree. They're widely used in many southeast Asian ethnic communities, such as people of Indian, Pakistani, Bangladeshi and Sri Lankan origin.
Betel nuts have a stimulant effect similar to coffee. They also have a carcinogenic effect, which can increase the risk of mouth cancer. This risk is increased by chewing betel nuts with tobacco, as many people in southeast Asia do.
Because of the tradition of using betel nuts, rates of mouth cancer are much higher in ethnic Indian, Pakistani, Bangladeshi and Sri Lankan communities than in the population at large.
Read more about south Asian health.
There's evidence that a poor diet may increase your risk of developing some types of mouth cancer.
Having a healthy, balanced diet that includes plenty of fruit and vegetables is thought to reduce your risk of developing mouth cancer.
Human papilloma virus (HPV)
The human papilloma virus (HPV) is a family of viruses that affect the skin and moist membranes that line the body, such as those in your cervix, anus, mouth and throat.
You can get an HPV infection by having sexual contact with a person who's already infected – you don't have to have "full" sex, just close skin-to-skin contact.
There's evidence that in rare cases, certain types of HPV can cause abnormal tissue growth inside the mouth, triggering mouth cancer.
As cancer is sometimes associated with long-standing wounds, there's a small chance that jagged, broken teeth, which cause persistent ulcers or wounds on the tongue, can increase the chance of mouth cancer developing there.
It's therefore very important to do everything you can to keep your mouth and teeth healthy.
Read more about dental health.
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 the back of the jaw
- through the lymphatic system – the lymphatic system is a series of vessels and glands spread throughout your body, which produce specialised cells needed by the immune system to fight infection
Mouth cancer that spreads to another part of the body is known as metastatic oral cancer, which are often called secondaries.
The lymph glands in the neck are usually the first place where mouth cancer forms secondaries.