Common causes of rectal bleeding include:
- Anal fissures (cuts)
- Inflammation (ulcerative colitis or irritable bowel disease)
- Colorectal polyps
- Colorectal cancer
- Diverticular disease
- Any upper gastrointestinal or small bowel lesion, if the bleeding is heavy.
In the lower digestive tract, the large intestine and rectum are frequent sites of bleeding. Hemorrhoids are the most common cause of visible blood in the digestive tract, especially blood that appears bright red. Hemorrhoids are enlarged veins in the anal area that can rupture and produce bright red blood, which can then show up in the toilet or on toilet paper. If red blood is seen, however, it is essential to exclude other causes of rectal bleeding, since the anal area may also be the site of cuts (fissures), inflammation, or cancer.
Benign (noncancerous) growths or polyps of the colon are common, and are thought to be possible forerunners of cancer. These growths can cause either bright red blood or occult bleeding (hidden bleeding). Colorectal cancer is the third most common cancer in the United States, and often causes occult bleeding at some point, but not necessarily visible rectal bleeding.
Inflammation from various causes can produce extensive bleeding from the colon. Different intestinal infections can cause inflammation and bloody diarrhea. Ulcerative colitis can produce inflammation and extensive surface bleeding from tiny ulcerations. Crohn's disease of the large intestine can also produce rectal bleeding.
Diverticular disease caused by pouches in the colon wall can result in massive bleeding.
Finally, as a person gets older, abnormalities may develop in the blood vessels of the large intestine (this is called angiodysplasia). This may result in recurrent rectal bleeding.
People taking blood-thinning medications (such as warfarin) may have rectal bleeding, especially if they take drugs like aspirin.