Bowel polyps

Bowel polyps are growths that develop on the wall of the large intestine or rectum. They are not usually cancerous but they often need to be removed when they are discovered, as some can turn into bowel cancer.

What are bowel polyps?

Polyps are growths that develop in your large intestine (bowel or colon) or the rectum (anus or bottom). They are usually less than 1 cm in size, although they can grow up to several centimetres. The exact cause of bowel polyps is not known. It's thought they're caused by the body producing too many cells in the lining of the bowel.

Below is a picture of your large intestine. The picture on the right is a close-up of a polyp which can be seen as a dark red ball.

Image credit: 123rf

There are different forms of polyps – some are a tiny raised area or bulge, some look like a grape on a stalk and others take the form of many tiny bumps clustered together. Some people just develop one polyp, while others may have a few.

Bowel polyps do not usually turn into cancer but, if some types of polyps (called adenomas) are not removed, there's a chance they may eventually become cancerous. But very few polyps will turn into bowel cancer, and it takes many years for this to happen. Read more about bowel cancer.

Doctors believe that most bowel cancers develop from adenoma polyps. Read more about the different types of polyps.

Who is at risk of getting bowel polyps?

You have a greater chance of developing polyps if you:

are over 50 years of age – 1 in 4 people aged over 50 have bowel polyps
are male – bowel polyps are slightly more common in men
have a family/whānau member with bowel polyps or bowel cancer
eat a lot of fatty food
smoke
drink alcohol
don't take regular exercise
are overweight
have a condition that affects your gut, eg, colitis, Crohn's disease or inflammatory bowel disease (IBD).

What are the symptoms of bowel polyps?

Most people with polyps are not aware they have them, as polyps don't usually produce symptoms. They are often discovered by accident. Some larger polyps can cause:

a small amount of rectal bleeding (blood in your poos)
mucus (slime) to be produced when you open your bowels
a change in your bowel habits, either diarrhoea (runny poos) or constipation
tummy pain.

How are polyps diagnosed?

Bowel polyps are usually found as a result of a bowel investigation for conditions like inflammatory bowel disease or bowel cancer. These investigations are done via a sigmoidoscopy to check the last part of your bowel, or a colonoscopy to check the whole length of your large bowel. Any polyps found are removed during the procedure and sent away to the laboratory for testing. If the polyps are found during a sigmoidoscopy, a colonoscopy may be needed to check the whole of your large bowel for polyps.

How are bowel polyps treated?

Bowel polyps can be removed by a procedure done during your colonoscopy.

For the procedure, the doctor passes a long wire loop through a colonoscope (a long, soft flexible tube containing a tiny video camera and a light) and around the base of the polyp. The loop is pulled tight, cutting off the polyp. You won't feel anything as your doctor will give you a medicine to numb the area first.
The polyp is removed from the body with a device.
An operation (surgery) is rarely needed to remove polyps but may be necessary if the polyps are very large or can't be reached safely during the colonoscopy.
After removal, the polyp is sent to a laboratory to check for any signs of cancer.

How often will I need to be checked for polyps?

How often you need to be checked for polyps depends on your risk factors for developing bowel cancer, your age and the type and number of polyps found during your investigations. The checks are done to find any more polyps that may develop and potentially turn into bowel cancer. Your doctor will give you more information on this.

Learn more

The following links provide further information on bowel polyps. Be aware that websites from other countries may contain information that differs from Aotearoa New Zealand recommendations.

Bowel polyps NHS Choices, UK, 2020
Bowel polyps Patient Info, UK, 2016
Bowel cancer – information for people at increased risk of bowel cancer NZ Guidelines Group, 2012
Familial Adenomatous Polyposis (FAP) New Zealand Familial GI Cancer Service