Why does rectal cancer cause change in bowel habits?

The rectum stores stool before it leaves the body. A tumour can reduce the space available, alter the rectum's ability to stretch, or irritate the lining. This may lead to constipation, looser stools, narrower stools, urgency, more frequent trips, or a feeling that the bowel has not emptied. Some people notice mucus or blood, cramping, or pressure in the pelvis.

Change in bowel habits has many possible causes, including infection, diet, medicines, irritable bowel conditions, and haemorrhoids. A bowel change alone does not establish rectal cancer. A clinician may assess the abdomen and rectum and may recommend stool tests, blood tests, endoscopy, or imaging depending on the pattern and duration.

Arrange a medical review for a new or persistent bowel change, particularly if it comes with blood in the stool, unexplained weight change, tiredness, abdominal or pelvic pain, or a feeling of incomplete emptying. Record stool frequency, consistency, bleeding, pain, and medicines. Do not rely on repeated laxatives or anti-diarrhoeal medicines without discussing the cause.

Seek urgent care for heavy rectal bleeding, black stools, severe or worsening abdominal pain, repeated vomiting, marked abdominal swelling, or inability to pass stool or gas. These symptoms can signal significant bleeding or bowel blockage and need prompt assessment.

Ask which tests fit your symptoms, whether an examination of the rectum is needed, and how to prepare for any endoscopy. Ask which bleeding, pain, or bowel changes should be reported urgently.