Blood in stool: color guide, causes and when to see a doctor

Rectal bleeding: Is it haemorrhoids or a sign of bowel cancer?

Used sheet of bloody toilet paper and a roll on white background, haemorrhoids and rectal bleeding concept.

It can feel both frightening and taboo to discover blood in the toilet bowl or on the paper after a bowel movement. But the fact is that rectal bleeding is a very common symptom that most people experience at some point in their lives.

Although the cause is often harmless - such as haemorrhoids - it is crucial never to ignore it. In this guide, we review the most common causes, the difference between symptoms, and why a bowel examination is your most important safeguard against bowel cancer. This article covers colours, causes and alarm symptoms. The work-up itself is described on the page about blood in stool.

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Why am I bleeding from the rectum?

There can be many causes of rectal bleeding. The colour of the blood and accompanying symptoms can often provide a clue as to where the bleeding originates.

1. Haemorrhoids (The most common cause)

Haemorrhoids are swollen blood vessels in or around the rectum (resembling small varicose veins). They typically bleed with fresh, bright red blood, which is seen on the surface of the stool or on the toilet paper.

• Symptoms: Itching, stinging, and a sensation of a lump at the anal opening.
• Severity: Harmless, but bothersome.

2. Anal Fissure (Tear at the anus)

A small tear in the lining of the anus, often caused by hard stools or constipation.

• Symptoms: Sharp, stabbing pains during and after bowel movements, along with fresh blood.

3. Bowel Cancer (Colorectal cancer)

This is the most serious cause. In this case, the blood is often darker and can be mixed into the stool itself.

• Symptoms: Changed bowel habits (alternating constipation and diarrhoea), unexplained weight loss, fatigue, and abdominal pain.
• Severity: Serious. The stage at diagnosis matters for prognosis and treatment options, and the course also depends on tumour factors and general health.

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When should I see a doctor?

Call 112 if heavy or ongoing rectal bleeding comes with dizziness, fainting, palpitations, pale clammy skin, or black tarry stools. That can be an acute bleed affecting the circulation and needs emergency hospital assessment, not a planned outpatient appointment.

Contact a doctor or the out-of-hours service the same day for black tarry stools without circulatory symptoms, large amounts of fresh blood, or bleeding with fever and severe abdominal pain.

Otherwise the rule is simple: rectal bleeding should always be investigated by a doctor the first time it occurs.

Even if you have had haemorrhoids before, new bleeding can mask other conditions. You should seek medical attention promptly if:

• Your stool changes shape or frequency for more than 4 weeks.
• You feel that the bowel is not emptying properly.
• The blood is dark or mixed with mucus.
• You feel unusually tired (signs of iron deficiency/anaemia).

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Bowel examination: What can I expect?

Many people are apprehensive about a bowel examination. Which examination is chosen depends on your symptoms, age, alarm features, test results and the overall medical assessment. An endoscopic examination can give important information about the cause of the bleeding, but no single examination can promise certainty, comfort or a complete answer.

1. Physical examination: The doctor feels with a finger (digital rectal examination) to check for haemorrhoids or lumps near the opening.
2. Endoscopy (Sigmoidoscopy or Colonoscopy): A thin, flexible tube with a camera is inserted into the bowel. Here, the doctor can see the lining directly and remove any polyps (precancerous growths) before they develop further.
3. Stool sample (FIT test): A test that checks for invisible blood in the stool. It is used to screen people without symptoms. A negative FIT does not rule out cancer in someone with visible rectal bleeding, so it does not replace endoscopy when symptoms are present.

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Frequently asked questions

Can stress cause blood in the stool? Stress can affect the stomach and bowel and cause abdominal pain, bloating and changed bowel habits, but stress does not in itself explain visible blood. If you see blood in your stool, it still needs to be assessed by a doctor.

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Prevention: Look after your bowel

You can reduce the risk of both haemorrhoids and bowel cancer through your lifestyle:

• High-fibre diet: Eat plenty of whole grains, vegetables, and fruit.
• Drink water: It keeps the stool soft and prevents tears.
• Physical activity: Exercise stimulates bowel movement (peristalsis).
• Go when you need to: Do not hold it in; this increases pressure in the rectum and can cause haemorrhoids.

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Differential diagnoses and further reading

Rectal bleeding has many possible causes, from benign conditions in the anal canal to inflammation or changes higher up in the bowel.

Haemorrhoids · Anal fissure · Inflammatory bowel disease (IBD)

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Sources and scientific background (PubMed)

To ensure correct information, we rely on the latest research and clinical guidelines:

• Background on haemorrhoids, pathophysiology, epidemiology and treatment: Lohsiriwat V. Hemorrhoids: from basic pathophysiology to clinical management. World J Gastroenterol 2012;18(17):2009-17. PubMed
• Background on colorectal cancer, including why screening programmes exist (the disease is preceded by a polypoid precursor): Kuipers EJ, Grady WM, Lieberman D, et al. Colorectal cancer. Nat Rev Dis Primers 2015;1:15065. PubMed
• Colorectal cancer, including colonoscopy as a screening method: Brenner H, Kloor M, Pox CP. Colorectal cancer. Lancet 2014;383(9927):1490-502. PubMed

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See also

Inflammatory bowel disease

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See also

Diverticula