Bleeding from the bowel has many causes, most of them treatable and many minor, such as piles. It should still be checked, because it can also be a sign of an ulcer, inflammation, polyps or cancer. Heavy bleeding, or black tarry stool with dizziness or fainting, is an emergency.

The colour gives a clue

• Bright red blood on the toilet paper or dripping into the toilet, separate from the stool: usually from near the anus, such as piles or a small tear (fissure)
• Darker red blood or clots mixed with the stool: often from higher up in the large bowel
• Black, sticky, tar-like stool with a strong smell (melaena): usually bleeding from the stomach or duodenum, with the blood digested on the way down
• Hidden (occult) blood: not visible, but found by a stool test or suspected because of iron-deficiency anaemia

These are only clues. Heavy bleeding from the stomach can pass quickly and look red, and bleeding from the right side of the large bowel can look dark.

Common causes

• Haemorrhoids (piles): painless bright red bleeding after a bowel movement, often with straining or constipation
• Anal fissure: a small tear causing sharp pain when passing stool and a streak of blood
• Polyps and bowel cancer: often painless; may cause anaemia or a change in bowel habit
• Inflammatory bowel disease or infection: bloody diarrhoea, urgency and mucus
• Diverticular bleeding: sudden, painless and sometimes heavy bleeding, mainly in older people
• Stomach or duodenal ulcers and inflammation, often linked to anti-inflammatory painkillers, aspirin or H. pylori: usually black stool
• Bleeding from enlarged veins in people with liver cirrhosis
• Abnormal small blood vessels in the bowel lining (angiodysplasia)

When it is not blood

• Iron tablets: dark green to black stools, but formed and not sticky
• Bismuth, found in some stomach medicines and H. pylori treatments: black stools
• Activated charcoal tablets: black stools
• Beetroot, red food colouring and some red drinks: red stools

If you are unsure whether the colour is blood, tell your doctor; a simple test can check.

Tests

• Examination, including a gentle internal examination of the back passage
• Blood count and iron levels
• Colonoscopy, especially if you are 45 or over, if your bowel habit has changed, if you are anaemic, or if a close relative has had bowel cancer. In younger people with typical bleeding from piles, a shorter examination (flexible sigmoidoscopy) may be enough
• Gastroscopy for black stools or vomiting blood
• In some settings, a stool test (FIT) to help decide how quickly a colonoscopy is needed
• If no source is found: a CT scan of the blood vessels, or capsule endoscopy of the small bowel

What you can do

• Do not assume bleeding is from piles, especially if it is new, you are 45 or over, or your bowel habit has changed
• Avoid constipation and straining: eat more fibre and drink enough fluid
• Avoid anti-inflammatory painkillers such as ibuprofen and diclofenac
• Do not stop aspirin or blood thinners on your own, but tell your doctor about the bleeding promptly
• Note the colour, amount and how often it happens; a photo can help your doctor

Common questions

This leaflet is general information and does not replace advice from your own doctor. Version 1.0, October 2026. Next review October 2028.