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Causes - Bowel cancer

We do not know the exact cause of bowel cancer. But there are some things that may make you more likely to get it.

Cancer happens when the cells in an area of your body divide and multiply too fast. This creates a lump of tissue known as a tumour.

Most cases of bowel cancer start inside clumps of cells called polyps. These are inside the lining of the bowel. Polyps can develop on the inner wall of the large intestine or rectum.

If you have bowel polyps, it does not always mean you'll get bowel cancer.

Bowel cancer risks

The main risk factors for bowel cancer are:


Around 1 in 20 people get bowel cancer. Almost 18 out of 20 cases of bowel cancer in Ireland are in people over 60.

Family history

Your risk of getting bowel cancer can increase if you have an immediate family member who had bowel cancer.

For example, your mother, father, brother or sister.

The risk is even bigger if they were under the age of 50.

You should talk to your GP if you're worried that your family's medical history may mean you're at a higher risk.

Your GP can refer you to a genetics specialist. They can give more advice about your level of risk and tests you can take to check it out.


If you eat a lot of red and processed meat, you can increase your risk of getting bowel cancer.

Research shows that if you eat a lot of fibre, it could help reduce your bowel cancer risk.

How to eat well


People who smoke cigarettes are more likely to get bowel cancer.

Help to quit smoking


There is a link between drinking alcohol and an increased risk of bowel cancer. Especially if you drink large amounts often.

Reduce your alcohol intake


Carrying extra weight or having obesity is linked to a higher risk of bowel cancer, especially in men.

Managing your weight may help lower your chances of getting cancer.

Treatment for obesity


People who are not physically active have a higher risk of getting bowel cancer.

You can help reduce your risk by being active every day.

How to increase your activity levels

Digestive disorders

Bowel cancer is more common in people who have conditions affecting the bowel.

For example, Crohn's disease or ulcerative colitis.

About 8 to 10 years after you first have symptoms of these conditions you will start to have check-ups.

You will have a colonoscopy to look for signs of bowel cancer.

How often you have a colonoscopy will depend on:

  • how long you have the condition
  • how severe your ulcerative colitis is
  • you family history of bowel cancer

Genetic conditions

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

Familial adenomatous polyposis (FAP)

This causes non-cancerous polyps to grow in your bowel.

Polyps caused by FAP are non-cancerous. But there's a high risk that over time at least one will turn cancerous.

Most people with FAP have bowel cancer by the time they're 50.

People with FAP are often advised by their doctor to have their large bowel removed before they reach the age of 25.

Lynch syndrome

Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome is an inherited gene fault (mutation). It increases your bowel cancer risk.

Removing the bowel is usually recommended for people with HNPCC.

Content supplied by the NHS and adapted for Ireland by the HSE

Page last reviewed: 11 October 2023
Next review due: 11 October 2026

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.