Light micrograph section through a human large bowel showing a colon polyp. Bowel polyps are small growths on the inner lining of the large intestine (colon) or rectum. They are very common, slightly more common in men, affecting around 1 in 4 people over the age of 50 years. These polyps do not usually cause any symptoms. However, larger polyps can cause rectal bleeding, diarrhoea, constipation and abdominal pain. If some types of polyps (called adenomas) are not removed, there is a chance they could become cancerous.