Blood in Stool (Anal Bleeding): Causes, Symptoms and When to Worry

Blood in the stool, on toilet paper, or in the toilet bowl is most often caused by haemorrhoids or anal fissures, both of which are treatable. It can also be the first sign of colorectal polyps or colorectal cancer. Any bleeding that persists beyond a week, recurs, or comes with other symptoms should be assessed by a doctor.

As a colorectal surgeon practising in Singapore for over 15 years, rectal bleeding is one of the most common reasons patients come to see me. In this article, I explain what causes anal bleeding, what the colour of the blood suggests, the warning signs I take seriously in clinic, and how I investigate and treat it.

Why I Never Dismiss Blood in the Stool

Most rectal bleeding turns out to be benign. The reason I assess every case properly is simple: colorectal cancer is one of the most common cancers in Singapore, and rectal bleeding from an early cancer can look identical to bleeding from haemorrhoids. I have seen patients who self-treated “piles” for months while a rectal tumour was the actual source. Confirming the cause, rather than assuming it, is the entire point of an assessment.

What Causes Anal Bleeding?

Haemorrhoids (Piles)

Haemorrhoids are swollen blood vessels in the rectum or anus, usually caused by straining during bowel movements, chronic constipation, prolonged sitting, or pregnancy. They are the most common cause of bright red bleeding I see in clinic. The blood is typically painless, coats the stool or drips into the bowl, and appears fresh.

Anal Fissures

An anal fissure is a small tear in the lining of the anus, usually from passing a hard or large stool. The hallmark is sharp pain during and after bowel movements, with small amounts of bright red blood on the toilet paper.

Colorectal Polyps and Colorectal Cancer

Colon polyps are growths on the lining of the colon or rectum. Most are benign, but some types can develop into colorectal cancer over time, which is why I remove polyps when I find them during colonoscopy. Both polyps and cancers can bleed, sometimes visibly and sometimes in amounts only detectable on a stool test. Bleeding from cancer may be accompanied by a change in bowel habit, unexplained weight loss, or fatigue from anaemia, though early cancers often cause no other symptoms at all.

Diverticular Disease

Diverticular disease involves small pouches (diverticula) forming in the colon wall, more common with age. A blood vessel at the neck of a pouch can erode and bleed, sometimes suddenly and in larger volumes. Diverticular bleeding is typically painless and ranges from dark red to maroon. When the pouches become inflamed instead, the result is diverticulitis, which usually presents with pain and fever rather than bleeding.

Inflammatory Bowel Disease (IBD)

Crohn’s disease and ulcerative colitis cause chronic inflammation of the digestive tract. During flare-ups, the inflamed lining ulcerates and bleeds, typically with diarrhoea, mucus, urgency, and abdominal cramping.

Other Causes

Less common causes include perianal abscesses and anal fistulas, proctitis (inflammation of the rectum), rectal ulcers, and infections. Bleeding can also originate higher in the digestive tract; I cover this under gastrointestinal bleeding.

What the Colour of the Blood Tells Me

The colour and pattern of bleeding gives me a starting point for where the blood is coming from. It is a clue, not a diagnosis.

Bright red blood usually comes from the anus or rectum: haemorrhoids, fissures, or, less commonly, a rectal polyp or cancer. It coats the stool, drips into the bowl, or appears on toilet paper.

Dark red or maroon blood, often mixed through the stool, suggests bleeding from higher in the colon, such as diverticular disease, polyps, or a tumour on the right side of the colon.

Black, tarry stools (melaena) indicate bleeding from the upper digestive tract, typically the stomach or duodenum, such as from an ulcer. The blood turns black as it is digested on its way through. This pattern needs prompt assessment, and the investigation usually includes a gastroscopy rather than starting with a colonoscopy.

One caution I always give patients: a very brisk bleed from the upper tract can still appear as red blood from below, and a slow lower bleed may not be visible at all. Colour alone is never enough to rule anything in or out.

Symptoms That Change My Level of Concern

When a patient describes rectal bleeding, these accompanying features determine how urgently I investigate:

• Pain during bowel movements points towards an anal fissure or thrombosed haemorrhoid.
• A change in bowel habit, such as new constipation, diarrhoea, narrower stools, or a feeling of incomplete emptying lasting more than a few weeks.
• Unexplained weight loss or persistent fatigue, which can reflect anaemia from chronic blood loss or an underlying cancer.
• Abdominal pain or cramping, which suggests a condition affecting the bowel itself, such as IBD or diverticular disease.
• A family history of colorectal cancer or polyps, which raises baseline risk regardless of symptoms.

How I Diagnose the Cause of Anal Bleeding

Consultation and Examination

I start with a detailed history: the colour and pattern of bleeding, bowel habit, diet, medications (blood thinners matter here), and family history. A physical examination includes inspection of the anus and a digital rectal examination, which identifies most fissures, external haemorrhoids, and low rectal masses within minutes.

Proctoscopy

A proctoscopy is a brief clinic-based examination of the anal canal and lower rectum. It allows me to directly see internal haemorrhoids and confirm whether they are the bleeding source.

Colonoscopy

A colonoscopy is the definitive investigation for rectal bleeding. It examines the entire colon and rectum, and allows me to remove polyps and take biopsies during the same procedure. I recommend it for any patient with persistent or unexplained bleeding, anyone aged 45 and above with new bleeding, and patients with risk factors such as a family history of colorectal cancer. Patients often ask about fees, which I have set out in a separate guide to colonoscopy costs in Singapore.

Stool and Blood Tests

The faecal immunochemical test (FIT) detects hidden blood in the stool and is the basis of Singapore’s national colorectal cancer screening programme for those aged 50 and above. A positive FIT result always warrants a colonoscopy. Blood tests check for anaemia from chronic blood loss.

Imaging

CT scans or CT colonography have a role when colonoscopy is not feasible or when I need to assess complications such as diverticulitis.

Treatment Options for Anal Bleeding

Treatment is directed at the cause, not the bleeding itself.

Non-Surgical Treatment

Dietary and lifestyle measures. Increasing fibre and fluid intake and avoiding straining resolves a substantial proportion of haemorrhoid and fissure bleeding without any procedure.

Medication. Topical creams and suppositories reduce inflammation and discomfort in haemorrhoids and fissures. Fissures may also be treated with ointments that relax the anal sphincter. IBD requires dedicated anti-inflammatory or immunomodulating medication.

Rubber band ligation. For persistent internal haemorrhoids, I place a small band at the base of the haemorrhoid during a clinic visit, cutting off its blood supply so it shrinks and detaches.

Surgical Treatment

Haemorrhoidectomy. For large or recurrent haemorrhoids that have not responded to other measures, surgical removal addresses the source of bleeding directly. I discuss the options, including the associated costs of haemorrhoid surgery, during consultation.

Lateral sphincterotomy. For chronic anal fissures that fail medical treatment, this procedure releases excess tension in the internal sphincter muscle so the tear can heal.

Abscess drainage and fistula surgery. Infected collections are drained, and fistula tracts are treated surgically.

Colectomy or bowel resection. For colorectal cancer and some cases of severe diverticular disease, removal of the affected segment of colon is required. My primary platform for this is robotic-assisted surgery, with laparoscopic and open approaches used where appropriate.

When to See a Doctor

Go to the A&E immediately if there is heavy or continuous bleeding, black tarry stools with weakness, dizziness, fainting, or a racing heartbeat. These suggest significant blood loss.

See a doctor promptly if bleeding persists beyond a week or keeps recurring, if you are 45 or older with new bleeding, or if bleeding comes with a change in bowel habit, weight loss, fatigue, or a family history of colorectal cancer.

Even minor bleeding deserves a check if it does not settle. The consultation is brief, and most causes are straightforward to treat once confirmed.

In Singapore, if you are 50 or above and have never been screened, do not wait for symptoms. The national screening programme recommends a yearly FIT test or a screening colonoscopy, because polyps and early cancers usually bleed before they cause anything you would notice.

Frequently Asked Questions

Is blood in the stool always serious?

No. Most rectal bleeding is caused by haemorrhoids or anal fissures, which are benign and treatable. Because bleeding from colorectal cancer can look identical, bleeding that persists beyond a week, recurs, or comes with other symptoms should always be properly assessed rather than assumed to be piles.

Can haemorrhoids cause blood in the stool?

Yes. Haemorrhoids are the most common cause of bright red rectal bleeding. The blood is typically painless and seen on toilet paper, coating the stool, or dripping into the bowl. A diagnosis of haemorrhoids should be confirmed by examination, since other conditions can produce the same pattern of bleeding.

What colour of blood is most concerning?

Black, tarry stools (melaena) suggest bleeding from the stomach or duodenum and need prompt medical attention. Dark red or maroon blood mixed through the stool suggests bleeding from within the colon. Bright red blood usually comes from the anus or rectum. All persistent bleeding warrants assessment regardless of colour.

When should I see a doctor about rectal bleeding?

See a doctor if bleeding lasts more than a week, keeps returning, or is accompanied by a change in bowel habit, weight loss, fatigue, or abdominal pain. Go to the A&E immediately for heavy bleeding, black tarry stools, dizziness, or fainting. If you are 45 or older, new bleeding should be assessed even without other symptoms.

Do I need a colonoscopy for blood in my stool?

Not always, but it is the definitive way to find the source of bleeding. I recommend a colonoscopy for persistent or unexplained bleeding, patients aged 45 and above with new bleeding, anyone with a positive FIT screening result, and those with a family history of colorectal cancer or polyps.

Can younger people get colorectal cancer?

Yes. While risk rises with age, colorectal cancer in adults below 50 has been increasing worldwide, and I do see it in younger patients. Age alone is not a reason to dismiss persistent rectal bleeding, particularly with a family history of colorectal cancer or polyps.

Will anal bleeding stop on its own?

Bleeding from minor haemorrhoids or fissures often settles with fibre, fluids, and avoiding straining. The risk of waiting is that bleeding from a polyp or cancer can also be intermittent, which falsely reassures people. If bleeding recurs or persists beyond a week, have it assessed.

Conclusion

Anal bleeding has many causes, and most of them are benign. The cause should be confirmed, not assumed, because the benign and the serious can look exactly the same in the toilet bowl. A proper assessment is quick, and treatment, once the diagnosis is clear, is usually straightforward.

If you are experiencing persistent or unexplained blood in your stool, schedule a consultation or contact my clinic on +65 8491 1525 for an assessment and a personalised treatment plan.