Patient Guide

IBS or Bowel Cancer? How to Tell the Difference

Irritable bowel syndrome (IBS) and bowel cancer can share several symptoms, which is why many patients, and sometimes their GPs, find it difficult to distinguish between the two. This article explains the key differences, and when symptoms should prompt further investigation.

What Is IBS?

IBS is a common, long-term condition that affects the digestive system. It causes symptoms such as abdominal cramping, bloating, diarrhoea and constipation. IBS is a functional disorder. There is no structural abnormality in the bowel, and it does not cause cancer or lead to serious complications. It typically affects younger adults and is more common in women.

Symptoms of IBS are often triggered or worsened by stress, diet or hormonal changes. They tend to fluctuate over time and are usually present for years before a patient seeks help.

What Is Bowel Cancer?

Bowel cancer (colorectal cancer) is a cancer arising from the lining of the colon or rectum. It is the fourth most common cancer in the UK. Unlike IBS, bowel cancer involves a structural change in the bowel, a tumour, which can be detected by colonoscopy, CT scan or other investigations.

Overlapping Symptoms

Both conditions can cause changes in bowel habit, abdominal discomfort and bloating. This overlap is why symptoms alone cannot reliably distinguish between the two, and why investigation is sometimes necessary.

Red Flag Symptoms That Need Urgent Assessment

Certain symptoms should never be attributed to IBS without further investigation, particularly in patients over 40 or those with a family history of bowel cancer:

  • Blood in the stool or rectal bleeding
  • A persistent change in bowel habit lasting more than four weeks
  • Unexplained weight loss
  • A feeling of incomplete emptying after opening your bowels
  • Abdominal or rectal pain that is new, persistent or worsening
  • Anaemia (low iron) without an obvious cause
  • A palpable abdominal or rectal mass
Blood in the stool is never normal and should always be investigated, even if haemorrhoids or another benign cause seems likely. It is not something to leave uninvestigated.

Key Differences Between IBS and Bowel Cancer

IBS typically begins before the age of 50, symptoms fluctuate and have often been present for years, there is no bleeding, no weight loss and no anaemia, and symptoms are often related to stress or diet. Bowel cancer more commonly presents after the age of 50 (though it can occur at any age), symptoms are progressive and new, and is often associated with bleeding, weight loss or anaemia.

What Should You Do?

If you have any of the red flag symptoms listed above, you should seek a specialist opinion promptly. Even if you have a known diagnosis of IBS, new symptoms that are different from your usual pattern warrant assessment.

Mr Kumar sees many patients who have been reassured that their symptoms are IBS, only for investigation to reveal a different diagnosis. A colonoscopy or flexible sigmoidoscopy can provide a definitive answer quickly and safely.

A private colonoscopy with Mr Kumar can be arranged within days, providing reassurance or an early diagnosis when it matters most.