Blood in your stool usually comes from somewhere along your digestive tract, and the cause ranges from something minor like hemorrhoids to something that needs prompt treatment like inflammatory bowel disease or colon cancer. The most common culprits are hemorrhoids, anal fissures, and diverticulosis, but the color, amount, and pattern of bleeding all offer clues about what’s going on and how seriously to take it.
What the Color of the Blood Tells You
Bright red blood on the toilet paper or in the bowl generally points to bleeding in the lower part of your digestive tract: the colon, rectum, or anus. Small amounts of bright red blood often come from anorectal problems like hemorrhoids, fissures, or small polyps. Larger volumes of bright red blood are more commonly linked to diverticulosis or abnormal blood vessels in the colon wall.
Black, tarry, sticky stool with a strong odor is a different signal. It typically means the bleeding started higher up in the digestive system, above the colon, often in the stomach or upper small intestine. Blood turns dark as it travels through the gut and gets partially digested. If your stool looks like this, the source is usually something like a stomach ulcer rather than a rectal problem.
One important caveat: not everything that looks like blood actually is. Beets and foods with red coloring can make stool appear reddish. Iron supplements, black licorice, blueberries, activated charcoal, and bismuth-based medications like Pepto-Bismol can all turn stool black. If you’ve recently consumed any of these, that may explain the color change entirely.
Hemorrhoids and Anal Fissures
Hemorrhoids are swollen blood vessels in or around the anus, and they’re one of the most frequent reasons people notice blood after a bowel movement. The bleeding is typically bright red, painless, and shows up on toilet paper or dripping into the bowl. Straining during constipation, sitting for long periods, and pregnancy all increase the likelihood of hemorrhoids.
Anal fissures are small tears in the lining of the anus, usually caused by passing hard or large stools. Unlike hemorrhoids, fissures tend to hurt, sometimes sharply, during and after a bowel movement. Both conditions cause intermittent bleeding that comes and goes, and both generally improve with dietary changes, more fiber, and adequate water intake.
Diverticulosis
Diverticulosis means small pouches have formed along the wall of your colon. It’s extremely common, especially after age 40, and most people with it never have symptoms. The pouches only cause problems if one bleeds or gets infected. When bleeding does happen, something injures a blood vessel inside the pouch, though the exact trigger isn’t well understood. Diverticular bleeding tends to be intense for a short period but usually stops on its own. It accounts for 25% to 60% of cases where lower gastrointestinal bleeding is significant enough to affect blood pressure or require medical attention.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract, and bloody stool is one of their hallmark symptoms. Ulcerative colitis specifically targets the lining of the large intestine and rectum, producing ulcers that bleed. Crohn’s disease can affect any part of the digestive tract and causes deeper inflammation in the tissue walls.
With either condition, you’ll typically notice other symptoms alongside the bleeding: persistent diarrhea, abdominal cramping, fatigue, and unintended weight loss. These are long-term conditions that require ongoing management, and bloody stool is often what prompts people to get diagnosed in the first place.
Infections That Cause Bloody Stool
Certain bacterial infections can inflame the intestinal lining enough to cause bleeding. One of the best-known is E. coli O157:H7, a strain that produces a toxin damaging the lining of the small intestine. Symptoms include watery diarrhea that may turn bloody, stomach cramps, and vomiting. In young children, this particular strain has been linked to kidney damage.
C. difficile is another common culprit, especially after a course of antibiotics. It causes a type of colon inflammation called pseudomembranous colitis, which can produce bloody diarrhea along with fever and abdominal pain. Bacterial dysentery from Salmonella or Shigella can also cause bloody stools. If your symptoms started suddenly, especially after eating undercooked food or traveling, an infection is a strong possibility.
Polyps and Colorectal Cancer
Colon polyps are small growths on the inner lining of the colon. Most are harmless, but some can bleed, and over time certain types can develop into cancer. Polyps and early-stage colorectal cancer often cause no noticeable symptoms, which is why screening matters so much. When they do bleed, the amount is often too small to see with the naked eye.
The U.S. Preventive Services Task Force recommends colorectal cancer screening starting at age 45 for all adults, continuing through age 75. Several screening options exist. A stool-based test called a fecal immunochemical test (FIT) uses antibodies to detect hidden blood in your stool and is done yearly. A colonoscopy, which uses a thin tube with a camera to examine the entire colon, is recommended every 10 years. If your doctor finds polyps during a colonoscopy, they can typically remove them on the spot, which prevents them from ever becoming cancerous.
Less Common Causes
Ischemic colitis happens when blood flow to part of the colon is temporarily reduced, causing inflammation and sometimes bleeding. It’s more common in older adults and people with cardiovascular disease. Radiation therapy to the pelvic area can also damage the rectal lining and cause bleeding that may appear weeks or months after treatment. A solitary rectal ulcer, though rare, is another possible source, typically associated with chronic straining or problems with how the pelvic floor muscles coordinate during bowel movements.
What to Track Before Your Appointment
If you’re planning to see a doctor about rectal bleeding, paying attention to a few details beforehand makes the visit more productive. Note the color of the blood (bright red, dark red, or black), whether it’s mixed into the stool or only on the surface, and roughly how much there is. Track how often it happens and whether it coincides with any changes in your bowel habits, like new constipation or diarrhea.
It also helps to describe the form of your stool. Hard, pebble-like stools suggest constipation, which can point toward fissures or hemorrhoids. Watery or mushy stools suggest diarrhea, which may indicate infection or inflammation. Recording these patterns for even a few days gives your doctor a much clearer picture of what’s going on.
Signs That Need Immediate Attention
Most rectal bleeding turns out to be something manageable, but certain combinations of symptoms signal a potential emergency. Heavy or continuous bleeding that doesn’t stop, especially paired with severe abdominal pain, warrants a trip to the emergency room. If you experience rapid or shallow breathing, dizziness when standing, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output alongside rectal bleeding, call 911. These are signs of shock, meaning your body is losing blood faster than it can compensate.
For bleeding that’s mild but persists for more than a day or two, scheduling a doctor’s visit is the right move. Even if the cause turns out to be benign, getting it checked rules out conditions that benefit from early treatment.