Blood in your stool: what it means, and when to worry
Seeing blood is frightening, and most of the time the cause is minor — piles and small tears account for the majority. But some patterns need same-day care, so this article leads with those rather than burying them.
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Get same-day medical help if any of these apply
- Heavy bleeding, or bleeding you cannot stop.
- Black, sticky, tar-like stool with a strong smell.
- Large blood clots, or the toilet water turning deep red.
- Bleeding with severe abdominal pain.
- Bleeding with dizziness, fainting, a racing heart, or feeling cold and clammy — these can be signs of significant blood loss.
In the UK that means calling 111, or 999 for heavy bleeding. Elsewhere, urgent care or an emergency department. This is the one situation where waiting to see whether it settles is the wrong call.
If none of that applies, you are almost certainly in the ordinary category — and the rest of this article is about telling those apart properly rather than guessing.
Why the colour matters
Colour is a rough guide to distance. Blood changes as it travels through the digestive tract, so the further it has come, the darker and more altered it looks by the time you see it.
| What you see | Where it probably came from | What to do |
|---|---|---|
| Bright red, on the paper or the surface | Very low down — anus or rectum | Common; see a GP if it persists past a day or two |
| Dark red or maroon, mixed through the stool | Higher in the colon | Get seen promptly rather than waiting |
| Black, tarry, sticky | Stomach or small intestine | Urgent — same day |
| Red streaks with obvious straining or pain | A fissure or haemorrhoid | Common; still worth confirming |
Two honest caveats. First, colour is suggestive, not diagnostic — fast bleeding from higher up can still look red. Second, plenty of things stain stool without any blood involved: beetroot and red food colouring for red; iron tablets, black liquorice and bismuth medicines for black. If you ate or took any of those, say so — it saves everyone a week of worry.
The common causes
In rough order of how often they turn out to be the answer:
- Haemorrhoids (piles). Swollen veins in the anus. Bright red blood, often on the paper, sometimes itching or a lump. Extremely common, particularly after pregnancy, heavy lifting or a stretch of constipation.
- Anal fissures. A small tear, usually from passing something hard. Sharp, stinging pain during and after, with a little bright red blood. The pain is often the giveaway.
- Constipation and straining. Not a cause in itself so much as what produces the two above. Worth reading our piece on what actually relieves constipation.
- Gastroenteritis. An infection can inflame the bowel enough to bleed a little, usually alongside diarrhoea.
- Inflammatory bowel disease. Crohn's or ulcerative colitis — typically blood with mucus, urgency, and a pattern over weeks rather than a one-off.
- Polyps and bowel cancer. Much less common than the above, and much more important not to miss. This is why persistent or painless bleeding gets investigated rather than reassured.
Notice that the top three are mechanical and the bottom three are not. That distinction is roughly what a doctor is trying to establish.
When it needs a GP rather than a wait
Separate from the urgent list, these are the patterns that mean “book something” instead of “keep an eye on it”:
- It has lasted more than a day or two, or keeps returning.
- It is painless. Counter-intuitively, painless bleeding is more worth investigating than painful bleeding — pain usually points at a fissure or pile.
- Blood is mixed evenly through the stool rather than sitting on the surface.
- It comes with weight loss you cannot explain, ongoing abdominal pain, or a change in your bowel habit lasting weeks.
- You are over 45 and have not had bowel screening.
- You have a family history of bowel cancer or IBD.
- You feel unusually tired or breathless — slow blood loss over time can cause anaemia.
None of these means something is seriously wrong. They are the combinations where the cost of checking is a short appointment, and the cost of not checking is occasionally much higher.
What the appointment usually involves
Worth knowing in advance, because not knowing puts people off going.
Expect questions about colour, timing, pain, your usual pattern, medication and family history. Often a brief examination. Frequently a stool sample — in the UK this is usually a FIT test, which looks for blood invisible to the eye and is done at home. Depending on your age and what is found, possibly a referral for a colonoscopy, which is a camera examination under sedation.
The examination is brief and undignified and everyone involved does it many times a day. It is not a reason to put this off.
What to write down before you go
Ten-minute appointments reward preparation, and this is a symptom people consistently under-report because it is embarrassing and intermittent.
- Dates. Every episode, not just the last one.
- Colour, and whether it was on the paper, in the bowl, or through the stool.
- Roughly how much — streaks, a teaspoon, more.
- Pain, and whether it was during or after.
- Your stool form around those days — the Bristol Stool Chart gives you language for this.
- Anything you are taking, including iron and anti-inflammatories.
Dookie Deluxe records all of that with a date attached, and exports it as a PDF you can hand over. That is the whole reason the export exists — not because an app can tell you what is wrong, but because “three times in the last fortnight, bright red, no pain” is a far better starting point than trying to remember under pressure.
The bottom line
Most rectal bleeding is haemorrhoids or a fissure and resolves. Some is not. The distinguishing features are not subtle — black or tarry, heavy, painless, persistent, mixed through, or alongside weight loss — and all of them are reasons to be seen rather than reassured by an article.
See a doctor promptly if you notice any of these
- Blood in your stool — bright red, or black and tar-like.
- Unexplained weight loss alongside a change in your bowels.
- A persistent change in habit lasting more than a few weeks.
- Persistent pain, vomiting, or a fever with the change.
- Pale stools with yellow skin or eyes and dark urine.
- A family history of bowel cancer or IBD, or you are over 45 and something has changed.
None of these mean something is seriously wrong — most have ordinary explanations. They are simply the ones worth getting looked at rather than watched.
Track it, don’t guess it
Dookie Deluxe logs type, colour, symptoms and timing in seconds — then turns weeks of entries into a pattern you (and your doctor) can actually read.
Common questions
Is blood in stool always serious?
No. The most common causes by a wide margin are haemorrhoids and anal fissures — small tears — both of which are uncomfortable rather than dangerous. But “usually minor” is not “always minor”, and the only way to tell them apart is to be seen.
What does black tarry stool mean?
Black, sticky, tar-like stool with a strong smell is called melaena, and it usually means blood from higher up the digestive tract — the stomach or small intestine — that has been digested on the way through. This needs urgent medical attention rather than a routine appointment. Iron tablets and Pepto-Bismol also blacken stool, which is why it matters to mention anything you are taking.
Can haemorrhoids cause a lot of blood?
They can cause more than you would expect — bright red blood on the paper, in the bowl, or streaking the stool. What haemorrhoids do not usually cause is blood mixed evenly through the stool, or blood with weight loss or a lasting change in bowel habit. Those combinations need investigating.
How long should I wait before seeing someone?
If bleeding is heavy, black and tarry, or comes with severe pain, dizziness or fainting, do not wait at all. Otherwise the usual guidance is to be seen if it lasts more than a day or two, or if it keeps coming back — and sooner if you are over 45, have never had bowel screening, or something else has changed alongside it.
Should I take photos or keep a record?
A dated record genuinely helps, and clinicians ask for exactly this. Note the colour, whether it was on the paper or mixed through, how much, and what else was happening — pain, straining, a change in your usual pattern. It turns “a while ago, a few times” into something a doctor can work with.