Blood in the stool can be alarming, but it often has a harmless cause, such as haemorrhoids or small tears at the anal opening. Nevertheless, the cause should always be clarified by a doctor to be sure. The blood may appear bright red on the surface of the stool or may darken the stool.
Possible causes
Haemorrhoids
Enlarged vascular cushions at the anal opening bleed easily, often showing up as bright red streaks on the stool or on the paper. They are a common and usually harmless cause.
Anal fissures
Small tears in the lining, for example from hard stools, can cause bright red blood and burning. They often heal on their own.
Polyps and colorectal cancer
Benign growths of the lining (polyps) and colorectal cancer can bleed, often unnoticed and mixed into the stool. Both are a key reason why blood in the stool is investigated — polyps can usually be removed straight away during a colonoscopy, before they can turn into cancer.
Inflammatory bowel disease
Ulcerative colitis and Crohn's disease cause diarrhoea with blood and mucus, often together with abdominal pain, weight loss, and symptoms lasting weeks to months.
Diverticular bleeding
Pouches in the wall of the large intestine can suddenly release larger amounts of blood without pain. This mainly affects older people.
Typical steps at the doctor's office
- 1In the consultation, you will be asked about the colour and amount of blood, your bowel habits, and any accompanying symptoms.
- 2The abdomen is palpated and the rectal area is examined to narrow down the cause.
- 3A colonoscopy may be useful for further assessment, allowing the lining to be examined directly.
What makes serious causes more likely
- The likelihood of polyps and colorectal cancer increases with age.
- Colorectal cancer or polyps in parents, siblings, or children, as well as certain hereditary forms of colorectal cancer, significantly increase the risk.
- A known chronic inflammatory bowel disease increases the risk the longer it has been present.
- Smoking, high alcohol consumption, being overweight, and lack of exercise are among the modifiable risk factors.
- A change in bowel habits lasting several weeks, unintentional weight loss, or newly detected anaemia together with blood in the stool make an assessment particularly urgent.
What typically happens next?
Bleeding from haemorrhoids and anal fissures usually improves within days to a few weeks once the stool becomes softer, but it often comes back. What matters is this: even if a harmless cause seems likely and the bleeding stops, this does not replace the need for assessment — bleeding from the rectum can mask a cause higher up. After a normal colonoscopy, you should seek assessment again if blood reappears or if your bowel habits change permanently.
What you can do yourself
- Aim for soft stools, for example through a fibre-rich diet and adequate fluid intake.
- Avoid straining hard during bowel movements and respond to the urge to go without delaying it.
- Clean the anal area gently and carefully to keep irritation to a minimum.
- Monitor your symptoms and note any changes to discuss with your doctor.
Black, tar-like stool, vomiting blood or larger amounts of blood together with weakness, dizziness or heart racing are an emergency: 144. Any other blood in the stool should always be medically assessed, even if a benign cause is likely. Contact the general practitioner's office or gastroenterology to have the cause reliably determined.
Frequently asked questions
- Is blood in stool always dangerous?
- No, harmless causes such as hemorrhoids are often responsible. Nevertheless, medical evaluation is important to safely rule out other causes.
- Is a colonoscopy always necessary?
- Not in every case. Your doctor will decide whether a colonoscopy is appropriate based on the findings, your age, and other symptoms in consultation with you.
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