Blood in the stool usually has a simple cause, such as piles (haemorrhoids) or an anal fissure (a small tear in the anus); but it is sometimes a sign of a polyp, bowel inflammation or bowel cancer [5]. Bright red blood usually comes from the anus or the end of the bowel, and black, tar-like stools usually come from bleeding in the stomach [6]; but the colour of the blood or the shape of the stool alone does not show whether cancer is present [2, 4]. If you are 40 or older, or if the bleeding comes with a change in bowel habit, weight loss, anaemia or a family history of bowel cancer, tell your doctor so that your bowel can be checked [3, 5].
Key points
- Most bleeding is not cancer: in studies, about 8 in 100 people aged 50 or over who saw their GP with bleeding from the back passage had bowel cancer; that is high enough for bleeding always to be checked [2].
- Painless bright red blood is a common sign of piles; but bowel polyps can also bleed without pain [5].
- Black, shiny, tar-like stools usually mean bleeding from the stomach or the first part of the small bowel and need urgent assessment [6]. Iron tablets and medicines containing bismuth can also darken the stool; this darkening is usually temporary and harmless [7, 8].
- From the age of 40, bleeding from the back passage is assessed with a full examination of the bowel (usually a colonoscopy), unless your bowel was examined and found normal in the past 10 years [5].
Blood in stool without pain: what does it mean?
The colour of the blood helps to guess where in the digestive tract the bleeding comes from. Blood from the left side and end of the large bowel or from the anus is usually bright red. Blood from the right side of the large bowel is often dark or maroon and mixed in with the stool. Bleeding from the stomach or the first part of the small bowel usually makes the stool black and tar-like [6].
This table is only a general guide and does not replace an examination:
| What you see | Where it usually comes from | Common causes |
|---|---|---|
| Bright red blood on the toilet paper or on the surface of the stool, without pain | The anus or the end of the large bowel [6] | Internal piles; sometimes a polyp or cancer [5] |
| Bright red blood with sharp pain when opening the bowels | The anus [5] | An anal fissure (a small tear in the anus), often after hard stools and constipation [5, 11] |
| Dark or maroon blood mixed in with the stool | The right side of the large bowel or the small bowel [6] | A polyp, cancer or bowel inflammation [5, 6] |
| Bloody diarrhoea with tummy pain | The large bowel [5] | Bowel inflammation (inflammatory bowel disease) or a bowel infection [5, 10] |
| Black, shiny, sticky stools like tar | The stomach or the first part of the small bowel; sometimes the right side of the large bowel [6] | Bleeding from the upper digestive tract; seek care urgently [6] |
| Dark or black stools after starting iron tablets or a medicine containing bismuth | Not bleeding | A temporary, harmless effect of the medicine [7, 8] |
If black stools come with dizziness, severe weakness or a racing heart, do not put them down to a medicine: go to an emergency department straight away.
Sometimes the bleeding is so slight that it cannot be seen. This hidden bleeding is usually found through iron-deficiency anaemia or a positive faecal occult blood test [6]. If your stool test was positive, read: My faecal occult blood test was positive. What should I do?
Piles or bowel cancer: what is the difference?
Piles (haemorrhoids) are swollen blood vessels inside and around the anus. Internal piles usually bleed without pain: streaks of bright red blood on the stool or on the toilet paper. Sometimes they also cause a lump that comes out, itching or discharge. This bleeding rarely causes anaemia [5]. Straining because of constipation, long-lasting diarrhoea, excess weight, pregnancy and a low-fibre diet make piles more likely [5].
The problem is that many people put any bleeding down to piles, when it may have another cause [5]. Bowel polyps can also bleed without pain. Bowel cancer may come with bleeding, pain, a change in bowel habit and weight loss [5]. That is why the decision to examine the bowel depends on your age and your other symptoms [5]:
- Under 40: if you have no warning signs (such as weight loss, tummy pain, fever or signs of anaemia), neither you nor your family has a history of bowel cancer or inflammatory bowel disease, and the bleeding settles with treatment for piles, a colonoscopy is usually not needed. But follow-up with your doctor matters, because bowel cancer has become more common in young adults.
- 40 or older, or younger with a risk factor: a full examination of the bowel with a colonoscopy (or a CT scan of the bowel), unless your bowel was examined and found normal in the past 10 years.
Read more: Colon polyps: types, cancer risk and when to repeat colonoscopy
What does colon cancer stool look like?
Bowel cancer can cause these changes [1]:
- bright red or very dark blood in the stool
- a change in bowel habit: diarrhoea, constipation, or a feeling that the bowel does not empty completely
- stools that are narrower than usual or have a different shape
- tummy discomfort such as cramps, bloating, wind or a feeling of fullness
- unexplained weight loss and tiredness
But the shape of the stool on its own is not a reliable sign. In studies, blood in the stool and anaemia were the most important signs, and the risk with most other symptoms was lower when they occurred alone; several symptoms together, though, are worth checking [2]. A stool test shows far more accurately than symptoms who should be examined sooner [4]. Read the full list of symptoms in What are the symptoms of bowel cancer?
IBS vs colon cancer: how do they differ?
| More in keeping with IBS | Needs further tests | |
|---|---|---|
| Tummy pain | Eased by opening the bowels, or linked to a change in how often you go or in the shape of the stool [9] | New pain with unexplained weight loss, especially from the age of 40 [3] |
| How long symptoms last | Pain, bloating or a change in bowel habit for at least 6 months [9] | A change in bowel habit from what is normal for you [3] |
| Other symptoms | Bloating, straining or urgency, symptoms worse after eating, mucus in the stool [9] | Blood in the stool, iron-deficiency anaemia, a lump in the tummy [3] |
| Tests | Blood count, inflammation tests and the test for coeliac disease are normal [9] | Anaemia or signs of inflammation in blood tests [3, 9] |
If you have symptoms of IBS, your doctor should also look for the warning signs of cancer; if any of them is present, further tests are needed [9].
How does a FIT stool test help?
The FIT (faecal immunochemical test) finds very small amounts of blood in the stool. In the UK, this test is done for adults with specific bowel symptoms to work out who needs urgent assessment [3, 4]. Someone with a lump in the anus or rectum is referred directly, without this test [3].
- If the result is high: you should be referred urgently for a bowel examination (usually a colonoscopy); do not put it off [3].
- If the result is low: bowel cancer is very unlikely [4]. But if your symptoms continue, see your doctor again; a negative test on its own is not a reason to rule out further tests [3, 4].
Blood in the stool in children and in pregnancy
Children: one common cause is an anal fissure, a small tear in the anus that comes with painful bowel movements and a little blood. Hard stools play an important part in causing it, which is why treating constipation matters to stop it coming back [11]. In newborns and babies, too, blood in the stool usually has a harmless, short-lived cause, such as a fissure, an infection or a food allergy; but it sometimes has a more serious cause [12]. Always have a doctor check blood in a child's stool, and seek care urgently if the child is drowsy, has a fever or has a swollen tummy.
Pregnancy: bleeding from the back passage is common in pregnancy. It is usually from piles or a fissure, which pregnancy makes worse [10]. But more serious causes such as inflammatory bowel disease or cancer should not be overlooked. Most tests are safe in pregnancy and should not be delayed for this reason [10].
When should I call my doctor?
Do not keep bleeding to yourself out of embarrassment or because you assume it is piles. See a doctor within the next few days if you have:
- new or repeated bleeding from the back passage and you are 40 or older [5]
- bleeding with a change in bowel habit, tummy pain or unexplained weight loss [3]
- iron-deficiency anaemia on a blood test [3]
- a history of bowel cancer or inflammatory bowel disease in yourself or in a parent, sibling or child [5]
- bleeding that has not settled with treatment for piles [5]
- a lump or sore in the anus with no known cause [3]
Heavy bleeding or large clots of blood, black tar-like stools, vomiting blood or material that looks like coffee grounds, dizziness, fainting or a racing heart need urgent care: call your local emergency number.
Frequently asked questions
I see red blood on the toilet paper after a bowel movement. Should I worry?
Bright red blood on the toilet paper or streaks of blood on the stool, especially without pain, usually come from piles or an anal fissure [5, 6]. If you are young, have no warning signs and it gets better with treatment for piles, further tests are usually not needed; but if you are 40 or older, or the bleeding continues, tell your doctor so that your bowel can be checked [5].
My stool has turned black. Does that mean I am bleeding?
Black, shiny, sticky stools like tar usually mean bleeding from the stomach or the first part of the small bowel; show this to a doctor urgently [6]. But iron tablets and medicines containing bismuth can also darken the stool, and this darkening is harmless [7, 8]. Read about the causes of bleeding from the stomach: Stomach ulcer, gastritis or stomach cancer: how can you tell?
Does colon cancer cause pain?
Not always. Bowel cancer can bleed without pain, or cause tummy discomfort such as cramps, wind and bloating [1]. Tummy pain on its own is less often a sign of cancer: in studies, about 3 in 100 people who saw their GP with tummy pain had bowel cancer [2]. Pain that is new and comes with weight loss or bleeding should be checked [3].
I am young. Could the blood in my stool be from cancer?
In young adults, bleeding from the back passage is often caused by piles [4]. But bowel cancer has become more common in young adults [5]; so if you have warning signs, or the bleeding does not settle with treatment, do not put off having it checked [5]. Read more: Bowel cancer in young adults: symptoms and why it is rising and What are the symptoms of bowel cancer?
My faecal occult blood test was negative. Can I stop worrying?
A negative result makes bowel cancer very unlikely [4]. But if your symptoms continue, see your doctor again: guidelines say further tests should not be ruled out on the basis of this test result alone [3, 4]. For repeated bleeding from the back passage, an examination of the lower bowel with a camera is suggested even when the result is low [4].
I do not see any blood, but I have anaemia. Could it be from my bowel?
Yes, it could. Slight, hidden bleeding from the bowel usually cannot be seen and is found only through iron-deficiency anaemia or a stool test [6]. In studies, about 1 in 10 people who saw their GP with anaemia had bowel cancer [2]. The UK national guideline recommends a stool test, followed by a bowel examination when needed, for adults with iron-deficiency anaemia [3].
I have a family history of bowel cancer. What should I do?
If a first-degree relative has had bowel cancer, take bleeding seriously even at a young age; in that case a full examination of the bowel is recommended [5]. For when to start screening without symptoms, read: At what age is a screening colonoscopy needed? and Is cancer hereditary?
Predictive value of symptoms and referral criteria (for doctors)
For physicians
Predictive value of rectal bleeding in primary care. In the systematic review and meta-analysis by Astin et al. (23 studies, symptomatic primary care patients only), the PPV of rectal bleeding ranged from 2.2% to 16% in 13 studies, with a pooled estimate of 8.1% (95% CI 6.0 to 11) in those aged 50 and over. The pooled PPV was 3.3% (0.7 to 16) for abdominal pain and 9.7% (3.5 to 27) for anaemia. The positive likelihood ratio for rectal bleeding with weight loss was 1.9 (1.3 to 2.8) and with a change in bowel habit 1.8 (1.3 to 2.5), but it was one or less for rectal bleeding with abdominal pain, diarrhoea or constipation [2].
NICE NG12 (2023 recommendations, adapted from DG56). Quantitative FIT (HM-JACKarc or OC-Sensor) for adults with an abdominal mass, a change in bowel habit, iron-deficiency anaemia, aged 40 and over with unexplained weight loss and abdominal pain, aged under 50 with rectal bleeding and either unexplained abdominal pain or weight loss, aged 50 and over with any of unexplained rectal bleeding, abdominal pain or weight loss, and aged 60 and over with anaemia even in the absence of iron deficiency (1.3.1). Suspected cancer pathway referral with a FIT result of at least 10 micrograms of haemoglobin per gram of faeces (1.3.2). With FIT below 10 or no sample returned: safety netting, and referral should not be delayed if there is strong clinical concern (1.3.3). A rectal mass, an unexplained anal mass or unexplained anal ulceration is referred without FIT (1.3.1, 1.3.5 and 1.3.6) [3].
ACPGBI/BSG guideline (2022). An fHb threshold of ≥10 µg/g for the urgent referral pathway; patients should not be excluded from referral on the basis of FIT alone; patients with fHb below 10 and persistent, unexplained symptoms causing ongoing clinical concern should be referred; for persistent or recurrent rectal bleeding with fHb below 10, flexible sigmoidoscopy is suggested (weak recommendation, very low-quality evidence). In the supporting meta-analysis, at a threshold of ≥10 (15 studies, 48,872 patients) the pooled sensitivity was 87.0% (81.0 to 91.6) and specificity 84.4% (79.4 to 88.3); the NPV in symptomatic patients meeting the UK two-week-wait criteria was consistently above 98.5%, and 99.5 to 99.6% in the largest studies [4].
Bleeding attributed to haemorrhoids. Under 40 without red flags (weight loss, abdominal pain, fever, signs of anaemia), without a personal or family history of CRC or IBD and responding to medical treatment, endoscopic evaluation is not required, but close follow-up is; over 40, and younger patients with risk factors: full colonic evaluation (colonoscopy or CT colonography) unless a normal evaluation within the past 10 years [5]. Melaena usually has an upper GI source, but bleeding from the right colon or small bowel can also cause melaena, and colonoscopy should be considered in melaena to exclude a right-sided colonic source; haematochezia is occasionally the presentation of a brisk upper GI bleed [6].
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References
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Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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- 4Faecal immunochemical testing (FIT) in patients with signs or symptoms of suspected colorectal cancer (CRC): a joint guideline from the Association of Coloproctology of Great Britain and Ireland (ACPGBI) and the British Society of Gastroenterology (BSG)
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- 12Rectal Bleeding in Infants: Diagnostic Work-up and Management
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