Rectal Bleeding – A discussion about possible causes

A nice post about the causes and investigations of rectal bleeding.

Editor’s note, August 2026. This post says colorectal screening begins at 50. The USPSTF lowered that to 45 in 2021, and several stool-based and visual options now sit alongside colonoscopy. Everything else here about the causes of rectal bleeding is unchanged.

Labelled diagram of the large intestine showing the cecum, ascending, transverse, descending and sigmoid colon, and the rectum — Anatomy of the large intestine. Image: OpenStax College, Anatomy and Physiology, CC BY 3.0.

One of the more common problems that brought patients in to see me, believe it or not, was seeing blood in the toilet, on the stool, or on the toilet paper after a bowel movement. Since I had seen several patients about this, I thought I would write about some of the possible causes.

Healthcare providers take this seriously, because blood noticed after a bowel movement can sometimes be a sign of colon or rectal cancer. Fortunately, most causes of rectal bleeding are not cancer.

Causes of rectal bleeding: