Cancer occurs when the cells in a certain area of your body divide and multiply too rapidly. This produces a lump of tissue known as a tumour.

Most cases of bowel cancer first develop inside clumps of cells on the inner lining of the bowel. These clumps are known as polyps. However, if you develop polyps, it does not necessarily mean you will get bowel cancer.

Exactly what causes cancer to develop inside the bowel is still unknown. However, research has shown several factors may make you more likely to develop it. These factors are outlined below.

Age

Your chances of developing bowel cancer increase as you get older. Almost nine out of 10 cases of bowel cancer in the UK are diagnosed in people over 60 years of age.

Family history

Having a family history of bowel cancer can increase your risk of developing the condition yourself, particularly if a close relative (mother, father, brother or sister) was diagnosed with bowel cancer below the age of 50.

If you are particularly concerned that your family's medical history may mean you are at an increased risk of developing bowel cancer, it may help to speak to your GP.

If necessary, your GP can refer you to a genetics specialist who can offer more advice about your level of risk and recommend any necessary tests to periodically check for the condition.

Diet

A large body of evidence suggests a diet high in red and processed meat can increase your risk of developing bowel cancer. For this reason, the Department of Health advises people who eat more than 90 grams (cooked weight) of red and processed meat a day to cut down to 70 grams. Read more about red meat and bowel cancer risk.

There is also evidence suggesting that a diet high in fibre could help reduce your bowel cancer risk.

Read more about eating good food and a healthy diet.

Smoking

People who smoke cigarettes are more likely to develop bowel cancer, other types of cancer and other serious conditions such as heart disease than people who do not smoke.

Read more about stopping smoking

Alcohol

Drinking alcohol has been shown to be associated with an increased risk of bowel cancer, particularly if you regularly drink large amounts of it.

Read about drinking and alcohol for more information and tips on cutting down.

Obesity

Being overweight or obese is linked to an increased risk of bowel cancer, particularly in men.

If you are overweight or obese, losing weight may help lower your chances of developing the condition.

Inactivity

People who are physically inactive have a higher risk of developing bowel cancer.

You can help reduce your risk of bowel and other cancers by being physically active every day.

Read more about health and fitness.

Digestive disorders

Some conditions affecting the bowel may put you at a higher risk of developing bowel cancer. For example, bowel cancer is more common in people who have had severe Crohn’s disease or ulcerative colitis for many years.

If you have one of these conditions, you will usually have regular check-ups to look for signs of bowel cancer from about 10 years after your symptoms first develop.

Check-ups will involve examining your bowel with a colonoscope – a long, narrow flexible tube containing a small camera – that is inserted into your rectum. The frequency of the colonoscopy examinations will increase the longer you live with the condition, and will also depend on factors such as how severe your ulcerative colitis is and if you have a family history of bowel cancer.

Genetic conditions

There are two rare inherited conditions that can lead to bowel cancer. They are:

• familial adenomatous polyposis (FAP) – a condition that triggers the growth of non-cancerous polyps inside the bowel
• hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome – an inherited gene fault (mutation) that increases your bowel cancer risk

Although the polyps caused by FAP are non-cancerous, there is a high risk that, over time, at least one will turn cancerous. Most people with FAP will have bowel cancer by the time they are 50 years of age.

As people with FAP have such a high risk of getting bowel cancer, they are often advised by their doctor to have their large bowel removed by surgery before they reach the age of 25. Families affected can find support and advice from FAP registries such as the FAP registry provided by St Mark’s Hospital, London.

Removing the bowel as a precautionary measure is also usually recommended in people with HNPCC because the risk of developing bowel cancer is so high.

Want to know more?

• Beating Bowel Cancer: causes
• Bowel Cancer Information: family history
• Bowel Cancer UK: why do I need fibre in my diet?
• Cancer Research UK: food types and bowel cancer
• Cancer Research UK: risk factors
• Wellcome Trust: FAP, HNPCC and genetic testing