Blood in Stool: Common Causes, When to Worry and When a Colonoscopy Is Needed

Medically reviewed by Dr Usman Naeem, 24 Oct 2026.

What the colour can tell you

• Bright red blood on the paper, dripping into the toilet or streaked on the stool usually comes from near the back passage, such as piles (haemorrhoids) or a fissure
• Darker red or maroon blood mixed into the stool can come from higher up in the bowel
• Black, sticky, tar-like stools (melena) usually mean bleeding from the stomach or upper gut, such as an ulcer or varices. This needs urgent medical care
• Iron tablets and bismuth medicines can make stools dark or black, and beetroot can make them look red. If you are unsure, see a doctor

Common causes

• Piles (haemorrhoids): swollen veins at the back passage, often with painless bright red bleeding, especially with constipation or straining
• Anal fissure: a small tear, usually with sharp pain during and after passing stool
• Infection (dysentery), often with diarrhoea, fever and cramps
• Inflammatory bowel disease (ulcerative colitis or Crohn’s disease), often with diarrhoea, mucus and urgency
• Polyps and bowel cancer: less common, but more likely with age, a family history, weight loss or anaemia
• Diverticular disease and blood-vessel changes in the bowel, mainly in older people

When is a colonoscopy advised?

Colonoscopy is a test that looks at the whole large bowel with a thin flexible camera, and polyps can often be removed during the same test. Your doctor may advise one if you have:

• Bleeding and you are aged around 45 or older, or bleeding that keeps coming back at any age
• A change in bowel habit lasting more than a few weeks, such as looser or more frequent stools
• Weight loss, tiredness or anaemia (low haemoglobin or iron)
• A family history of bowel cancer or polyps, especially in a close relative diagnosed young
• Diarrhoea with blood and mucus that does not settle, suggesting colitis
• Bleeding that continues even after treatment for piles or fissure

What to expect at a visit

The doctor will ask about the bleeding, bowel habit, weight, medicines (especially blood thinners and painkillers) and family history, and will usually examine the back passage gently. Blood tests such as a full blood count may be done. Depending on the findings, a shorter test (proctoscopy or sigmoidoscopy) or a full colonoscopy may be advised. Please do not feel embarrassed: these are routine questions and examinations for a gastroenterologist.

While you wait for an appointment

• Avoid constipation and straining: increase fibre slowly, drink enough water and do not delay going to the toilet
• Do not stop blood thinners or aspirin on your own. Ask your doctor first
• Avoid assuming it is “just piles” if you are older, losing weight or the bleeding keeps returning
• Note how often it happens, the colour, and any change in bowel habit, to tell the doctor

Common questions

Related videos by Dr Usman Naeem

From Dr Usman Naeem’s own YouTube channel (mostly Urdu). They load only when you press play.

English

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General information only, not personal medical advice. Do not start or stop medicines because of this article. See the medical disclaimer.