Common causes of anal bleeding can include:
- Anal fissures
- Inflammation (such as ulcerative colitis or Crohn's disease)
- Colon polyps
- Colon cancer
- Rectal cancer
- Diverticular disease (diverticulitis)
- 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 anal 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 the toilet paper. If red blood is seen, however, it is essential to exclude other causes of anal bleeding, since the anal area may also be the site of cuts (fissures), inflammation, or cancer.
Benign growths, which are noncancerous, or polyps of the colon are common and are thought to be forerunners of cancer. These growths can cause either bright red blood or occult bleeding. Colorectal cancer is the third most common of all cancers in the United States and often causes occult bleeding at some point, but not necessarily visible anal 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 anal bleeding.
Diverticular disease caused by diverticula (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 (angiodysplasia). This may result in recurrent anal bleeding.
People taking blood-thinning medications (like warfarin) may have gastrointestinal bleeding, especially if they take drugs like aspirin.