Bowel polyps are small growths on the inner lining of the colon (large bowel) or rectum. They are common, affecting 15-20% of the UK population, and do not usually cause symptoms. 

Polyps are usually less than 1cm in size, although they can grow up to several centimetres. There are various forms:

• some are a tiny raised area or bulge, called a sessile polyp
• some look like a grape on a stalk, known as a pedunculated polyp
• some take the form of many tiny bumps clustered together

Bowel polyps are not usually cancerous, although they’ll need to be removed as some will eventually turn into cancer if left untreated (see box, left).

Some people just develop one polyp, while others may have a few. They tend to occur in people over the age of 60.

How are they caused?

Bowel polyps are caused by an abnormal production of cells. The lining of the bowel constantly renews itself and a faulty gene can cause the cells in the bowel lining to grow more quickly.

There may be a family tendency towards developing bowel polyps or bowel cancer.

What are the symptoms?

Most people with polyps won’t be aware of them as they produce no symptoms and are often discovered by accident.

However, some larger polyps can cause:

• a small amount of bleeding
• mucus to be produced when you open your bowels
• diarrhoea or constipation 
• abdominal pain

How are they discovered?

Bowel polyps are usually found as a result of a bowel investigation for another reason, such as a sigmoidoscopy (examination of the last part of the bowel) or barium enema (where a white liquid is passed into your bowel so a clear X-ray image can be taken).

If polyps are found, a colonoscopy is then needed to view the whole of the large bowel. Read about colonoscopies below.

How are they treated?

There are several methods for treating polyps, but the most common procedures are:

• Snaring the polyp while you have a colonoscopy. Snaring is like cutting the polyp off with a cheese wire, and is painless.
• Hot biopsying, which removes the polyp by touching it with an electric probe (also painless).

Both of the above methods involve passing a flexible instrument called a colonoscope through your bottom, up into your bowel. The colonoscope has a wire with an electric current to either cauterize (burn off) or snare the polyp.

A more unusual way to treat polyps is surgically removing part of the bowel – this is usually only done when the polyp has some cell changes or is particularly large. 

After the polyp or polyps have been removed, they are sent to specialist doctors in a laboratory who will inform your consultant if:

• the polyp has been completely removed
• there is any risk of it re-growing
• there is any cancerous change in the polyp

If there is cancerous change in the polyp, you may need further treatment (depending on the degree and extent of change). Your specialist will be able to advise you on this.

Outlook

Some people will need further colonoscopies because polyps can recur. Polyps can sometimes run in families – this is uncommon, but means you’ll need colonoscopy checks at regular intervals.

You might be asked to have repeat examinations at intervals of around three to five years, to catch any further polyps that may develop and potentially turn into bowel cancer.