Condition

Blood in the Stool

Never assume it is haemorrhoids — and 'you're too young for bowel cancer' is no longer true

Last reviewed: July 2026
Version: 1.0
Review cadence: Annually

What it is

Blood in the stool has many causes, and most of them are benign — haemorrhoids and anal fissures account for the large majority. But it is also the commonest presenting symptom of colorectal cancer, and the two things are not mutually exclusive: haemorrhoids are extremely common, so a person with bowel cancer very often ALSO has haemorrhoids, and finding one does not exclude the other. That is the entire reason this page exists. The safe rule is simple and it is the opposite of what most people do: rectal bleeding is investigated, not explained away.

Why it matters

Because the two ways this goes wrong both end in the same place. The first is self-diagnosis: it is bright red, it is on the paper, it must be piles — and it usually is, until the once in some number of times that it is not. The second is being dismissed, and this is now a serious and worsening problem: COLORECTAL CANCER INCIDENCE IS RISING SHARPLY IN PEOPLE UNDER 50, and young adults with rectal bleeding are still routinely reassured on the basis of age alone. 'You're too young for bowel cancer' was reasonable advice a generation ago. It is now the sentence that delays diagnoses in exactly the group whose cancers are rising, and it is worth going into a consultation prepared to push back on it.

The evidence

What BioSignal knows about treating this

Guideline-anchored clinical contextLast reviewed July 2026 · reviewed annually · 4 references

What works for Blood in the Stool

BioSignal’s clinical summary, most important first.

GET IT ASSESSED — do not self-diagnose haemorrhoids. Haemorrhoids are extremely common, which means people with bowel cancer very often have them too. Finding one does not exclude the other, and that single sentence is the reason this page exists
IF YOU ARE UNDER 50 AND YOU ARE TOLD YOU ARE TOO YOUNG, PUSH BACK — colorectal cancer is rising sharply in younger adults and reassurance based on age alone is no longer safe. Ask specifically for examination and a FIT test
BLACK, TARRY STOOL IS AN EMERGENCY — that is digested blood from the upper gut. Go to an emergency department, do not wait for an appointment
Do the FIT test if you are sent one, and take up bowel screening when invited — this is the intervention with the largest measured benefit available here
Check ferritin — iron deficiency from an unnoticed slow bleed is a common way bowel cancer presents, and it is missed when only haemoglobin is checked
Treat the benign cause once it is actually established — fibre, fluid, not straining, and topical treatment resolve most haemorrhoids and fissures
Do not stop an anticoagulant on your own — bleeding on a blood thinner still needs a cause found, and stopping the drug carries its own risk of stroke

Signal Records relevant to this condition

Interventions and contributing factors — some of these records describe a cause rather than a cure. The rating shown is BioSignal’s confidence in that Signal Record, not a claim about how well it treats this condition. Open any of them for the full evidence.

Start Here

New to this? Read these first

Typical Journey

How this usually unfolds

Recognize risk factors
Get diagnosed
Track key biomarkers
Lifestyle first
Evidence-based treatment
Long-term monitoring

An orientation to how this topic is typically approached — not medical advice.

Who is at risk

Age — risk rises with age, but incidence in the under-50s is RISING and age is no longer a safe reason for reassurance
Family history of bowel cancer or polyps
Inflammatory bowel disease (Crohn's, ulcerative colitis)
Lynch syndrome and familial adenomatous polyposis
Smoking, alcohol, obesity, processed meat, low fibre
Anticoagulant medication — which can unmask a lesion that was always there. Bleeding on a blood thinner is still bleeding that needs a cause
Constipation and straining — a genuine cause of the benign things, and not a reason to skip investigation

How it's diagnosed

The character of the bleeding narrows it, and it does not settle it. BRIGHT RED blood on the paper or coating the outside of the stool is usually anorectal — haemorrhoids or a fissure — and cannot be assumed to be. Blood MIXED INTO the stool, or a change in bowel habit, or weight loss, or anaemia, points higher and is far more concerning. BLACK, TARRY, foul-smelling stool (melaena) is digested blood from the upper gastrointestinal tract and is a medical emergency. Everyone with rectal bleeding warrants examination; most warrant a FIT test; and many warrant colonoscopy, which is the investigation that both diagnoses cancer and prevents it by removing polyps.

Clinical assessment and examination — including a rectal examination, which people dread and which finds things
FIT (faecal immunochemical test) — detects blood not visible to the eye, and is the basis of bowel cancer screening. A negative FIT is reassuring but does NOT override visible bleeding with worrying features
Full blood count and FERRITIN — iron deficiency from a slow, unnoticed bleed is a common presentation of bowel cancer, and ferritin falls before haemoglobin
COLONOSCOPY — the definitive investigation. It diagnoses cancer and it PREVENTS cancer, by removing the polyps that would have become one
Participation in bowel cancer screening when invited — it is the single most effective thing most adults can do here
RED FLAGS requiring urgent assessment: blood mixed into the stool, change in bowel habit lasting weeks, unexplained weight loss, iron deficiency anaemia, a lump, or black tarry stool

Most important

Key biomarkers

Ferritin High-Sensitivity CRP Faecal Calprotectin

Day to day

Lifestyle

Fibre and fluid prevent the straining that causes most benign anorectal bleeding — and prevention is not a substitute for investigating bleeding that has already happened
Do not sit and strain on the toilet for long periods
Take up bowel cancer screening when it is offered. It works

Explore

Explore this condition across BioSignal

Frequently asked questions

It's bright red and only on the paper. That's just piles, isn't it?

Probably — and 'probably' is not a diagnosis you should be making for yourself. Here is the trap, and it is a genuinely counter-intuitive one: haemorrhoids are SO common that a person with bowel cancer is very likely to have haemorrhoids as well. So finding piles proves nothing. Doctors have missed cancers this way and patients have missed them far more often. Bright red bleeding on the paper is usually benign, and the only way to know that it is benign in YOUR case is to have it looked at. This is not scaremongering: it is the difference between a five-minute examination and a delayed cancer.

I'm 32 and I've been told I'm too young for bowel cancer. Is that right?

It is increasingly not, and this deserves to be said plainly. Colorectal cancer incidence in adults under 50 has been RISING for years, for reasons that are not understood, and young people with rectal bleeding continue to be reassured on the basis of age and then diagnosed late. If you have persistent rectal bleeding, or blood mixed into the stool, or a change in bowel habit, or unexplained weight loss, or iron deficiency, being in your thirties is not a reason to be sent away. Ask directly for an examination and a FIT test, and say that you are aware incidence is rising in your age group. You are not being difficult. You are being accurate.

What does black or tarry stool mean?

It means blood has come from higher up — the stomach or duodenum — and has been digested on the way through, which is what turns it black and gives it a characteristic smell. This is called melaena and it is a MEDICAL EMERGENCY. It signals a significant upper gastrointestinal bleed, most often from a peptic ulcer or from varices. Go to an emergency department. Do not wait for a GP appointment, and do not wait to see whether it happens again. (One benign exception: iron tablets and bismuth also blacken the stool, but they do not make it tarry or foul-smelling — and if you are in any doubt at all, be assessed.)

I'm on a blood thinner. Doesn't that explain it?

It explains why you are bleeding MORE. It does not explain why you are bleeding at all. Anticoagulants do not create lesions; they unmask them — the polyp, the ulcer or the tumour was there, and the drug has revealed it. In practice, bleeding on an anticoagulant is a reason to investigate, not a reason to shrug. And do not stop the drug yourself: you are taking it because the risk of a stroke or a clot outweighs the bleeding risk, and that calculation does not pause while you decide. Tell a clinician, and let them make the call.

Should I do the bowel screening test?

Yes. Bowel cancer screening with the FIT test is one of the most effective preventive interventions offered by any health system, and uptake is far lower than it should be — mostly because the test involves a small stool sample and people put the envelope in a drawer. It detects blood you cannot see, at a stage where the cancer is curable, and colonoscopy after a positive FIT can remove the polyps that would have become cancers. It is a few minutes of mild unpleasantness against a disease that kills people who could have been caught early.

Evidence summary

Rectal bleeding is common and most often benign — haemorrhoids and anal fissures predominate — but it is also the commonest presenting symptom of colorectal cancer, and the high prevalence of benign anorectal disease means the presence of haemorrhoids does not exclude a synchronous malignancy. The incidence of early-onset colorectal cancer (under 50) has risen substantially over recent decades for reasons that remain unexplained, and diagnostic delay in this group is well documented and is associated with reassurance based on age. Faecal immunochemical testing (FIT) is an effective triage and screening tool; population screening programmes based on FIT reduce colorectal cancer mortality, and colonoscopy both diagnoses cancer and reduces incidence through polypectomy. Iron deficiency anaemia arising from occult gastrointestinal blood loss is an established presentation of colorectal malignancy, and ferritin falls before haemoglobin. Melaena indicates upper gastrointestinal bleeding and constitutes a medical emergency. Bleeding in a patient on anticoagulation requires investigation of the source rather than attribution to the drug.

References & sources

NICE NG12 — Suspected cancer: recognition and referral
NICE DG56 — Quantitative faecal immunochemical testing to guide referral for colorectal cancer
Randomized trials and cohort evidence for FIT-based bowel cancer screening and mortality reduction
Epidemiological studies of rising early-onset colorectal cancer incidence

Educational information — not medical advice

Condition pages orient you across the evidence; they don't diagnose or treat. Diagnosis and management belong with a qualified clinician. See our Medical Disclaimer.

Is this condition page clear, accurate, and useful? Your feedback shapes what we review next.

Give feedback