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Causes - Bowel cancer

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

Cancer happens when the cells in an 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 called polyps. These are on the inner lining of the bowel.

It doesn't always mean you'll get bowel cancer if you develop polyps.

Some polyps regress, and some don't change. Only a few grow and develop into bowel cancer over a period of several years.

The main risk factors for bowel cancer are outlined below.


Around 1 in 20 people develop bowel cancer. Almost 18 out of 20 cases of bowel cancer in Ireland are diagnosed in people over the age of 60.

Family history

Having a history of bowel cancer in a first-degree relative under 50 can increase your risk of developing the condition. A first-degree relative is a mother, father, brother or sister.

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

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


A diet high in red and processed meat can increase your risk of developing bowel cancer.

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

Eat more healthily


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

Help to stop smoking


Drinking alcohol has been shown to be linked with an increased risk of bowel cancer. Especially if you drink large amounts often.

Reduce your alcohol intake


Being overweight or obese is linked to a higher risk of bowel cancer, especially in men.

If you're overweight or obese, losing weight may help lower your chances of getting cancer.


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

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

Get more active

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 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 that contains a small camera. 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 if you have a family history of bowel cancer.

Genetic conditions

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

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

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 have 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.

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

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

Page last reviewed: 30 May 2019
Next review due: 30 May 2024

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