What causes rectal bleeding during bowel movements?

Rectal bleeding—i.e., the presence of blood in stool, or blood appearing before or after defecation—may manifest as bright red, dark red, or tarry (melena) blood. Causes of rectal bleeding are numerous and commonly include lower gastrointestinal disorders, upper gastrointestinal disorders, and systemic diseases. So, what causes rectal bleeding? Below, we address this question.

What Causes Rectal Bleeding?

1. Hemorrhoids

Hemorrhoids result from downward displacement of the anal cushions and varicosity of the hemorrhoidal veins. When prolapsed hemorrhoids are severe, hard fecal masses may lacerate the hemorrhoidal mucosa and underlying blood vessels during defecation, leading to bleeding. This bleeding may present as dripping or even a forceful spray, typically with bright-red blood. Additionally, patients often experience protrusion of a palpable mass during bleeding episodes.

2. Anal Fissure

Anal fissure is a common benign anorectal condition primarily caused by passage of large, hard stools that tear the perianal skin, resulting in bleeding and pain. Patients frequently report associated perianal pain and constipation. In addition to bleeding and pain, some individuals may notice discharge from the anal region—prompt medical evaluation and treatment are therefore recommended.

3. Gastrointestinal Diseases

(1) Colonic Disorders

Examples include colitis, ulcerative colitis, and colorectal cancer. In colitis, hematochezia (bright-red blood in stool) is a hallmark symptom, though patients may also experience mucus discharge, abdominal pain, fever, and increased bowel movement frequency. Colorectal cancer—a malignant neoplasm—commonly presents with dark-red or bright-red blood mixed in the stool, accompanied by a sensation of rectal fullness or tenesmus.

(2) Rectal Disorders

Rectal polyps may cause bleeding during defecation. Similarly, rectal cancer often manifests with hematochezia. Although patients typically do not experience anal pain during bowel movements, they may report persistent anal discomfort, which progressively worsens as the disease advances.

The above outlines the most common causes of rectal bleeding. Patients are advised to modify their dietary habits—for instance, increasing intake of fiber-rich, stool-softening foods—and consider adjunctive therapies such as pharmacologic treatment and sitz baths to help alleviate symptoms. We hope this information proves helpful.