The two leading causes of mouth cancer in the UK are drinking too much alcohol and smoking.

Both alcohol and tobacco 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.

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.

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 found throughout your body which 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.

Other risk factors

Other risk factors for mouth cancer may include:

• chewing tobacco or other smokeless tobacco products like snus
• chewing betel nuts with or without tobacco
• a poor diet
• the human papilloma virus (HPV)
• poor oral hygiene

Smokeless tobacco

There is a range of smokeless tobacco products including:

• 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

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

Diet

There is evidence that a poor diet may increase your risk of some types of mouth cancer.

A healthy, balanced diet with 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 your body, such as those in your cervix, anus, mouth and throat.

You can contract an 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.

There is evidence that in rare cases, certain types of HPV can cause abnormal tissue growth inside the mouth, triggering 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.