Blood in Stool? What Can Cause It?
A clear guide to understand the most common causes of rectal bleeding and when you should see a doctor
Understanding the causes of rectal bleeding
Quick Summary - The Essentials
✅ Most Common Causes:
- • Hemorrhoids: 64% of cases - most common
- • Diverticulosis: 30-38% - frequent in older adults
- • Polyps: 10-26% - important to detect them
- • Anal fissure: Causes intense pain
🚨 When to Seek Urgent Care:
- • Heavy or persistent bleeding
- • Dizziness, weakness, or paleness
- • Severe abdominal pain
- • Unexplained weight loss
Before you panic: A reassuring message
Seeing blood in your stool can be very frightening, but most of the time it's nothing serious. In fact, in more than 60% of cases it's due to hemorrhoids, which although bothersome, are not dangerous. What's important is knowing when to consult and what tests you need. In this article, I'll explain everything clearly and without technical jargon.
What exactly is rectal bleeding?
"Rectal bleeding" or "hematochezia" is the medical term for red blood that you see in your stool, on toilet paper, or in the toilet bowl. It's different from other forms of digestive bleeding because:
- It's bright red blood: This means it comes from areas close to the anus (colon, rectum), not from the stomach
- It's easily visible: It's not hidden or mixed with stool in a dark form
- It's usually alarming: Seeing blood is always scary, but it doesn't always indicate severity
Why does blood appear in stool?
Think of your intestine as a long, delicate hose. Any scratch, inflammation, or "little bump" inside can rupture and bleed when stool passes through. The good news is that most of these causes are benign and treatable.
The 6 most common causes (with real data)
Based on the most recent scientific studies, these are the causes that appear most frequently when someone consults for blood in stool:
Hemorrhoids
Prevalence: 28-64% of cases
What are they?
They are swollen veins in the rectum or anus, like varicose veins in the legs but in a different area. They become inflamed due to straining during bowel movements, pregnancy, sitting for long periods, or simply due to predisposition.
Characteristic symptoms:
- • Bright red blood when wiping
- • Generally does NOT hurt
- • Bleeding related to bowel movement
- • May have itching or sensation of a lump
Reassuring fact: Hemorrhoids are the cause in almost 2 out of 3 people who bleed from the rectum. They're bothersome but not dangerous and have effective treatment.
Diverticular disease
Prevalence: 30-38% of cases
What are they?
They're like small "pouches" that form in the wall of the large intestine over the years. They normally don't cause symptoms, but sometimes they can bleed.
Characteristic symptoms:
- • Heavy bleeding with sudden onset
- • Generally WITHOUT pain
- • More common in people over 60
- • Bleeding can be intermittent
Important: Diverticular bleeding usually looks more impressive, but in 80% of cases it stops on its own. Even so, it always requires medical evaluation.
Polyps and colorectal cancer
Prevalence: Polyps 10-26% | Cancer 2-17%
What are they?
Polyps are "little bumps" that grow on the colon wall. Most are benign, but some can turn into cancer over time. That's why it's SO important to detect and remove them.
Warning symptoms:
- • Intermittent or persistent bleeding
- • Changes in bowel habits
- • Unexplained weight loss
- • Fatigue or anemia
This is why colonoscopy is essential: It's the ONLY way to see polyps and cancer in early stages, when they're 100% curable. If you're over 50 in Europe (or 45 in the US) or have risk factors, you should get an endoscopic evaluation.
Anal fissure
Prevalence: <10% but very symptomatic
What is it?
It's a "crack" or tear in the skin of the anus, usually caused by constipation or very hard bowel movements. Think of it as a "paper cut" but in a very sensitive area.
Very characteristic symptoms:
- • INTENSE PAIN during bowel movement
- • Small amount of blood on toilet paper
- • Pain lasting hours afterward
- • Anal sphincter spasm
Good news: Anal fissure is painful but not serious. With medical treatment (creams, stool softeners) most heal within weeks.
Colitis (inflammatory or infectious)
Prevalence: 1-6% of cases
What is it?
Inflammation of the intestine that can be due to infection (viruses, bacteria) or chronic diseases like ulcerative colitis or Crohn's disease.
Associated symptoms:
- • Diarrhea with blood
- • Cramping abdominal pain
- • Fever (in infections)
- • Urgency to have bowel movement
Angiodysplasia and vascular causes
Prevalence: 1-2% of cases
What are they?
They are "weak blood vessels" in the colon wall that bleed easily. They're more common in elderly people or those taking anticoagulants.
Risk factors:
- • Age over 70 years
- • Use of anticoagulants
- • Kidney failure
- • Heart diseases
When should I worry and seek urgent care?
ALARM signals - Seek immediate care if you have:
🚨 Urgent symptoms:
- • Heavy and continuous bleeding
- • Dizziness or fainting
- • Extreme paleness
- • Rapid heart rate
- • Severe abdominal pain
⚠️ Important signals:
- • Bleeding lasting more than 2-3 days
- • Change in bowel habits
- • Unexplained weight loss
- • Age over 50 (first time in Europe) or 45 (in US)
- • Family history of cancer
My advice as a specialist
Although most of the time it's nothing serious, ALL blood in stool deserves an evaluation. Don't stay wondering or wait for it to get worse. A timely consultation can:
- ✓ Give you peace of mind if it's something benign
- ✓ Detect polyps before they turn into cancer
- ✓ Treat the problem early and effectively
Have you noticed blood in your stool?
As a specialist in advanced endoscopy, I can perform a complete evaluation and determine the exact cause of your bleeding. Don't stay wondering.
Book an AppointmentWhat tests do you need? Colonoscopy and more
Depending on your symptoms, age, and risk factors, these are the tests we may need:
Colonoscopy - The gold standard
It's the most complete and accurate test. It allows seeing the ENTIRE colon, taking biopsies, and removing polyps in the same procedure. In my practice, I perform high-quality endoscopies with sedation for your maximum comfort.
Fecal occult blood test (FOBT)
Detects microscopic blood that you can't see with the naked eye. It's useful for screening, but if you already see visible blood, you generally need colonoscopy directly.
Flexible sigmoidoscopy
Explores only the last 60 cm of the colon. Useful for clearly lower-source bleeding (hemorrhoids, fissures) in young people without risk factors.
Digital rectal exam and anoscopy
Allows evaluation of the anus and lower rectum for hemorrhoids, fissures, or palpable masses. It's part of the basic physical exam.
Preparing for your colonoscopy
Preparation is KEY to a successful colonoscopy. Good colon cleansing allows detection of even the smallest lesions. I recommend reading my complete guide:
Prevention: How to reduce the risk of rectal bleeding
Although not all causes can be prevented, there are measures that DO significantly reduce the risk:
High-fiber diet
Eat fruits, vegetables, legumes, and whole grains. Fiber keeps stool soft and reduces straining during bowel movements.
Adequate hydration
Drinking enough water helps stools stay soft and easy to pass, preventing hemorrhoids and fissures.
Regular exercise
Physical activity improves intestinal transit and reduces constipation, preventing hemorrhoids and diverticulosis.
Colorectal cancer screening
Colonoscopy from age 50 (Europe) or 45 (US) detects and removes polyps BEFORE they turn into cancer.
Conclusion: Don't panic, but don't ignore it either
Key messages to remember
Seeing blood in stool is scary, but in most cases it's nothing serious
✓ Act this way:
- 1. Don't panic - take a deep breath
- 2. Observe the characteristics of the bleeding
- 3. Consult a digestive specialist
- 4. Perform the recommended tests
- 5. Follow the indicated treatment
As a specialist in gastroenterology and advanced endoscopy, I've treated hundreds of patients with rectal bleeding. The vast majority had benign and treatable causes. What's important is not to stay wondering and to get a complete evaluation to rule out serious problems.
Remember: colorectal cancer is one of the few cancers that can be prevented almost 100% if we detect and remove polyps in time. A colonoscopy can save your life.
Do you have rectal bleeding and need evaluation?
I'll help you find the exact cause and the best treatment for your case. With experience in advanced endoscopy and minimally invasive techniques.
Book an AppointmentScientific References
- 1. Ashburn JH. Hemorrhoidal Disease. JAMA. 2025;:2837775. doi:10.1001/jama.2025.13083
- 2. Wald A, Bharucha AE, Limketkai B, et al. ACG Clinical Guidelines: Management of Benign Anorectal Disorders. The American Journal of Gastroenterology. 2021;116(10):1987-2008. doi:10.14309/ajg.0000000000001507
- 3. Calderwood AH, Shaukat A. Colorectal Cancer Screening and Surveillance and Other Colon Conditions in the Older Adult. The American Journal of Gastroenterology. 2025;120(Suppl 10):S8-S16. doi:10.14309/ajg.0000000000003641.02
- 4. Sengupta N, Feuerstein JD, Jairath V, et al. Management of Patients With Acute Lower Gastrointestinal Bleeding: An Updated ACG Guideline. The American Journal of Gastroenterology. 2023;118(2):208-231. doi:10.14309/ajg.0000000000002130
- 5. Metcalf JV, Smith J, Jones R, Record CO. Incidence and Causes of Rectal Bleeding in General Practice as Detected by Colonoscopy. The British Journal of General Practice. 1996;46(404):161-4.
- 6. Helfand M, Marton KI, Zimmer-Gembeck MJ, Sox HC. History of Visible Rectal Bleeding in a Primary Care Population. Initial Assessment and 10-Year Follow-Up. JAMA. 1997;277(1):44-8.
- 7. Demb J, Kolb JM, Dounel J, et al. Red Flag Signs and Symptoms for Patients With Early-Onset Colorectal Cancer: A Systematic Review and Meta-Analysis. JAMA Network Open. 2024;7(5):e2413157. doi:10.1001/jamanetworkopen.2024.13157
Dr. Pedro de María Pallarés
Gastroenterologist • Advanced Endoscopy Specialist
Hospital Universitario La Paz • INMEQ
🏆 TopDoctors Awards 2024 • Member SEPD, SEED, ESGE