The 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.
If you drink alcohol or you smoke, this increases your risk of mouth cancer. If you both smoke and drink alcohol, this further increases your risk.
It's not known exactly what triggers the DNA changes that lead to mouth cancer, or why only a small number of people develop it.
Other risk factors for mouth cancer include:
Smokeless tobacco products include:
Betel nuts are mildly addictive seeds from the betel palm tree. They're widely used in many south Asian 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 means they can increase the risk of mouth cancer. This risk is increased further by chewing betel nuts with added tobacco, as many people in south Asia do.
Because of the tradition of chewing betel nuts, rates of mouth cancer are much higher in people from the Indian, Pakistani, Bangladeshi and Sri Lankan community than in the British population at large.
There's evidence that an unhealthy diet can increase your risk of getting some types of mouth cancer.
The human papilloma virus (HPV) is a group of viruses that affect the skin and moist membranes inside the body, such as those in the cervix, anus, mouth and throat.
You can get an HPV infection by having sexual contact with a person who's already infected. You do not have to have penetrative sex, just 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 linked 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.
Find out more about how to take care of your teeth and gums.
There are 2 ways mouth cancer can spread:
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.