Causes

The exact cause of bowel cancer is unknown. However, research has shown several factors may make you more likely to develop it.

Cancer develops when the cells in a certain area of your body divide and multiply too quickly. This produces a lump of tissue called a tumour.

Bowel cancer usually first develops inside clumps of cells called polyps on the inner lining of the bowel.

However, it does not necessarily mean you'll get bowel cancer if you develop polyps.

Some polyps go away by themselves, and some do not change. Only a few grow and eventually develop into bowel cancer over a period of several years.

Age

More than 9 out of 10 cases of bowel cancer develop in older adults over the age of 50, and nearly 6 out of 10 cases develop in people aged 70 or older.

Family history

Having a family history of bowel cancer in a first-degree relative – a mother, father, brother or sister – under the age of 50 can increase your lifetime risk of developing the condition yourself.

If you're particularly concerned that your family's medical history may mean you're 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 give you 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 and Social Care recommends that people who eat more than 90g (cooked weight) a day of red and processed meat should cut down to 70g a day.

Read more about red meat and bowel cancer risk.

There's also evidence that suggests a diet high in fibre could help reduce your bowel cancer risk.

Read more about eating a healthy balanced diet.

Smoking

People who smoke cigarettes are more likely to develop bowel cancer, as well as other types of cancer and other serious conditions, such as heart disease.

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.

Read about these tips about cutting down on alcohol.

Obesity

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

If you're 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've had extensive Crohn's disease or ulcerative colitis for more than 10 years.

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

Check-ups involve examining your bowel with a colonoscope – a long, narrow flexible tube with a small camera at the end. This is inserted into your bottom.

The frequency of the colonoscopy examinations will increase the longer you live with the condition. This also depends on factors such as how severe your ulcerative colitis is and whether you have a family history of bowel cancer.

Genetic conditions

There are 2 rare inherited conditions that can lead to bowel cancer:

• 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's a high risk that over time at least 1 will turn cancerous. Most people with FAP have bowel cancer by the time they're 50.

As people with FAP have such a high risk of getting bowel cancer, they're often advised by their doctor to have their large bowel removed before they reach the age of 25.

Families affected can find support and advice from FAP registries such as The Polyposis Registry provided by St Mark's Hospital, London.

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

Further information

• Lynn's Bowel Cancer Campaign: family history
• Bowel Cancer UK: diet
• Cancer Research UK: risk and causes

Page last reviewed: Mon Oct 2022 Next review due: Wed Feb 2020