The exact cause of bowel cancer is not known. However, some factors increase the chance of developing bowel cancer.

Risk factors include:

  • Age – bowel cancer more commonly affects people over the age of 50.
  • Polyps – having a large nuber of polyps in the bowel.
  • Bowel diseases – people who have an inflammatory bowel disease, such as Crohn’s disease or ulcerative colitis, have a significantly increased risk, particularly if they have had it for more than 8 years.
  • Lifestyle factors – being overweight, having a diet high in red meat (particularly processed meats such as salami or ham), drinking alcohol and smoking increase the risk.
  • Other diseases – people who have had bowel cancer once are more likely to develop a second bowel cancer; some people who have had ovarian or endometrial cancer may have an increased risk of bowel cancer.
  • Strong family history – bowel cancer can run in the family.
  • Rare genetic disorders – such as familial adenomatous polyposis and Lynch syndrome.

Being physically active, maintaining a healthy weight and eating a high-fibre diet may help to protect against bowel cancer.

Family history of cancer

If one or more of your close family members (such as a parent or sibling) have had bowel cancer, it may increase your risk. This is especially the case if they were diagnosed before the age of 55, or if there are 2 close relatives on the same side of your family with bowel cancer.

A family history of other cancers, such as endometrial cancer, may also increase your risk of developing bowel cancer.

Inherited genetic conditions

There are two rare conditions that occur in some families. These cause a small number (5% to 6%) of bowel cancers.

Familial adenomatous polyposis (FAP)

This condition causes hundreds of polyps to form in the bowel. If polyps caused by FAP are not removed, they will become cancerous.

Lynch syndrome

Previously known as hereditary non-polyposis colorectal cancer (HNPCC), this syndrome is characterised by a fault in the gene that helps DNA repair itself. Having Lynch syndrome increases the risk of developing bowel cancer and other cancers.


In its early stages, bowel cancer often has no symptoms. This is why screening for bowel cancer is so important.

However, some people with bowel cancer do experience persistent symptoms. These can include:

  • a change in bowel habit, such as diarrhoea, constipation, or smaller, more frequent bowel movements
  • a change in appearance of bowel movements (e.g. narrower stools or mucus in stools)
  • a feeling of fullness or bloating in the bowel or rectum
  • a feeling that the bowel hasn’t emptied completely after a bowel movement
  • blood in the stools or on the toilet paper
  • unexplained weight loss
  • weakness or fatigue
  • rectal or anal pain
  • a lump in the rectum or anus
  • abdominal pain or swelling
  • a low red blood cell count (anaemia), which can cause tiredness and weakness.

Not everyone with these symptoms has bowel cancer. Other conditions, such as haemorrhoids, diverticulitis (inflammation of pouches in the bowel wall), or tears in the anal canal, and some foods or medications, can also cause these changes. In a small number of cases, similar symptoms may indicate anal cancer. This rare cancer is a different type of cancer to bowel cancer.

Short-term changes in bowel function are very common and usually do not indicate a serious problem. However, if you have any of the above symptoms for more than 4 weeks, see your doctor for a check-up.

Last Reviewed: 16/05/2016

Reproduced with the kind permission of The Cancer Council New South Wales.


Cancer Council NSW. Bowel Cancer. (accessed May 2016.)