VHOSPITAL.CLINIC · Medical Q&A

What Causes Blood in stool?

A complete overview of all potential causes of blood in stool, from benign to serious medical conditions.

What It Means

Blood in stool has many potential causes spanning multiple organ systems. A systematic approach — considering the character, timing, triggers, and associated symptoms — helps identify the most likely cause and guides appropriate management.

Common Causes

  • Infectious causes: viral, bacterial, or fungal pathogens triggering systemic or localised blood in stool
  • Inflammatory/autoimmune: the body's immune response producing blood in stool as a bystander effect
  • Metabolic: disorders of thyroid, adrenal, or blood glucose regulation
  • Structural/mechanical: nerve compression, joint damage, or organ enlargement
  • Underlying conditions: Colorectal Cancer, Stomach Cancer, Crohns Disease are among the leading identifiable causes

Red Flags — When to Act

  • Unintentional weight loss accompanying blood in stool (possible malignancy or metabolic disease)
  • Night sweats, fever, and blood in stool persisting >2 weeks
  • New blood in stool in someone with a known cancer, immunosuppression, or recent surgery
  • Rapid progression or change in the character of long-standing blood in stool
  • Family history of serious hereditary conditions presenting with blood in stool

What to Do Now

  1. 1.Keep a symptom diary: date, time, severity, triggers, and what improves or worsens blood in stool
  2. 2.Review your medications — many drugs can cause blood in stool as a side effect
  3. 3.Assess lifestyle factors: sleep, diet, alcohol, exercise, and hydration
  4. 4.Use our AI symptom checker to receive a structured differential and guidance
  5. 5.Book a GP appointment for persistent, recurring, or unexplained blood in stool

When to See a Doctor

  • Blood in stool persists beyond 1 week without an obvious cause
  • Severity is moderate-to-severe or worsening over time
  • Any red-flag features are present (see above)

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Frequently Asked Questions

What is the most common cause of blood in stool?

The most common causes of blood in stool in the general population are stress, dehydration, poor sleep, and minor infections. In specific populations, Colorectal Cancer and other underlying conditions account for a significant proportion of cases.

Can medications cause blood in stool?

Yes — many medications list blood in stool as a potential side effect. Common culprits include antihypertensives, antibiotics, NSAIDs, and hormonal treatments. Review your medication list with a pharmacist or doctor if you suspect a drug-related cause.

Is blood in stool always related to a physical cause?

No. Psychological conditions such as anxiety, depression, and stress disorders frequently produce genuine physical blood in stool through the mind-body axis. Psychosomatic blood in stool is a real, measurable phenomenon requiring appropriate treatment.

Related Resources

Possible Causes

  • Infectious causes: viral, bacterial, or fungal pathogens triggering systemic or localised blood in stool
  • Inflammatory/autoimmune: the body's immune response producing blood in stool as a bystander effect
  • Metabolic: disorders of thyroid, adrenal, or blood glucose regulation
  • Structural/mechanical: nerve compression, joint damage, or organ enlargement
blood in stoolFull symptom guide

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Medical ReviewvHospital Editorial Team · 2024–2025
Sources:WHOPubMedUpToDateNICE