Noticing blood when you go to the toilet can be alarming, but it is also very common and often has a harmless explanation. That said, blood in your stool should never simply be ignored. This guide explains the different types of bleeding, the usual causes, and the warning signs that mean you should see a doctor.
Visible versus hidden blood
Visible blood is the sort you can see, and its colour offers clues. Bright red blood, often on the paper or in the bowl, usually comes from lower down, near the back passage. Dark, black or tarry stools suggest bleeding higher up in the digestive tract and need prompt attention.
Hidden blood is different. It is present in amounts too small to see, and it can only be picked up by a laboratory stool test such as a FIT. Hidden blood can be an early clue to changes in the bowel that have not yet caused any obvious symptom.
Common and usually harmless causes
Most bleeding, particularly bright red bleeding, comes from minor problems around the back passage.
- Haemorrhoids (piles) — swollen blood vessels that bleed easily
- Anal fissures — small tears in the skin, often after constipation
- Gastroenteritis — a temporary tummy bug causing irritation
These causes are frequent and usually settle, but they can look identical at first to conditions that need excluding.
Causes that need to be excluded
Some causes of bleeding are more serious and need to be ruled out. These include polyps (growths that can occasionally become cancerous), inflammatory bowel disease such as Crohn's or ulcerative colitis, and bowel cancer. A FIT test is often a useful first step here, because it detects hidden blood and helps decide who needs further investigation such as a colonoscopy.
Check for hidden blood
A FIT home test detects blood in the stool you cannot see — a simple first step, posted to you.
Check for hidden bloodRed flags that need prompt review
Please arrange to see your GP, urgently where relevant, if you notice any of the following:
- Bleeding that is persistent or keeps coming back
- Dark, black or tarry stools
- Unexplained weight loss
- A lasting change in your bowel habit
- Symptoms of anaemia such as tiredness, breathlessness or looking pale
When to see a doctor
Blood in the stool is common and often not serious, but it is not something to brush aside. A stool test can help build the picture, but it is only one part of it. If bleeding persists, recurs, or comes with any of the red flags above, see your GP so the cause can be properly assessed. Trust your instincts, and never feel it is too small a thing to check.
Check for hidden blood
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic