Blood in your stool can come from dozens of different sources along the digestive tract, ranging from a minor anal fissure to a serious condition like colorectal cancer. The most common cause by far, especially in younger adults and children, is a small tear in the skin around the anus. But the color, amount, and pattern of bleeding all offer clues about what’s going on and whether you need urgent care.
What the Color of the Blood Tells You
The shade of blood you see is one of the most useful pieces of information for narrowing down the source. Bright red blood typically means the bleeding is coming from the lower part of the digestive tract: the colon, rectum, or anus. Dark red or maroon blood suggests the source is higher up, in the upper colon or small intestine. Black, tarry stools point to bleeding in the stomach, where blood has been partially digested before passing through the rest of the system.
These aren’t absolute rules. A very fast bleed high in the digestive tract can still produce red blood because it moves through quickly. But in general, the darker the blood, the further it has traveled.
Hemorrhoids and Anal Fissures
These two conditions account for the majority of cases, particularly when the blood is bright red and shows up on toilet paper or on the surface of the stool. Hemorrhoids are swollen blood vessels in or around the anus. They often cause noticeable lumps, itching, and mild discomfort, but most hemorrhoids don’t actually cause pain. You might notice blood dripping into the toilet bowl after a bowel movement.
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. You may also feel a burning or itching sensation that lingers. In children, anal fissures are the cause of bloody stools roughly 90% of the time.
A doctor can typically diagnose either condition during a physical exam. If the source isn’t obvious from the outside, a closer look with a scope may be needed.
Diverticular Bleeding
Diverticulosis is a condition where small pouches form in the walls of the colon. It’s extremely common in people over 50 and usually causes no symptoms at all. Occasionally, though, a blood vessel near one of those pouches can rupture and produce a sudden, painless episode of bright or dark red bleeding that can look alarming.
The good news is that diverticular bleeding stops on its own in up to 90% of cases. Risk factors include physical inactivity, obesity, and the use of blood-thinning or anti-clotting medications. Men and older adults are more likely to experience it, and bleeding from pouches on the right side of the colon is significantly more common than from the left.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease are the two main forms of inflammatory bowel disease (IBD), and both can cause blood in the stool. Ulcerative colitis produces ulcers and chronic inflammation in the lining of the large intestine, often leading to bloody diarrhea, urgency, and cramping. Crohn’s disease can affect any part of the digestive tract and causes deeper inflammation that may result in blood mixed into the stool along with mucus.
IBD tends to follow a pattern of flare-ups and remissions. If you’re seeing blood alongside persistent diarrhea, abdominal pain, weight loss, or fatigue, these conditions are worth investigating. They’re typically diagnosed through a combination of blood tests, stool tests, and colonoscopy.
Colon Polyps and Colorectal Cancer
Polyps are small growths on the inner lining of the colon. Most are harmless, but some can slowly develop into cancer over a period of years. Both polyps and colorectal cancer can cause blood in the stool, often in amounts too small to see with the naked eye. When visible bleeding does occur, it may be dark red or mixed throughout the stool rather than sitting on the surface.
This is why screening matters even if you feel fine. The U.S. Preventive Services Task Force recommends that all adults begin colorectal cancer screening at age 45 and continue through age 75. Several options exist: a stool-based test done at home every one to three years, a flexible sigmoidoscopy every five to ten years, or a colonoscopy every ten years for people at average risk. Each approach has trade-offs in convenience and accuracy, but the most important thing is choosing one and sticking to the schedule.
Infections
Bacterial infections from organisms like Salmonella, E. coli, or Campylobacter can inflame the lining of the intestines enough to cause bloody diarrhea. These infections are usually tied to contaminated food or water and come on with cramping, fever, and frequent loose stools. Most resolve within a week, though some require treatment.
A specific type of colon infection called pseudomembranous colitis, often triggered by antibiotic use, can also produce bloody stools. This happens when antibiotics disrupt the normal balance of gut bacteria and allow harmful organisms to take over.
Medications That Increase Bleeding Risk
Several common drug classes raise the odds of gastrointestinal bleeding. Anti-inflammatory painkillers like ibuprofen and aspirin can irritate the stomach lining or worsen existing ulcers, leading to bleeding that shows up as black, tarry stools. Blood thinners (anticoagulants) and antiplatelet drugs don’t cause bleeding directly, but they make it harder for your body to stop a bleed once it starts, turning a minor issue into a more significant one.
If you take any of these medications regularly and notice a change in your stool color, that’s worth a conversation with your doctor. Iron supplements can also turn stools black, which can look like blood but isn’t. Certain foods, including beets and red-dyed foods, can mimic the appearance of blood as well.
Foods and Supplements That Mimic Blood
Not every red or dark stool contains blood. Beets, tomatoes, red gelatin, and red-colored drinks can all produce stool that looks bloody but is perfectly harmless. Iron supplements and bismuth-containing medications (the active ingredient in some stomach remedies) can turn stools black in a way that resembles digested blood.
If you’re unsure whether what you’re seeing is actually blood, think about what you’ve eaten in the past 24 to 48 hours. Stool tests can also distinguish real blood from dietary color changes. Before a fecal occult blood test, you may be asked to temporarily avoid rare red meat, certain fruits and vegetables, vitamin C, iron supplements, and painkillers like aspirin or ibuprofen, since all of these can interfere with results.
Causes in Infants and Children
Blood in a child’s stool understandably causes alarm, but the explanation is usually simple. Anal fissures from constipation are responsible in about 90% of pediatric cases, producing streaks of bright red blood on the outside of the stool or on the diaper.
In babies under two months old, a condition called cow’s milk colitis can cause loose, slimy, blood-streaked stools. It’s a reaction to proteins in cow’s milk-based formula (or occasionally to dairy in a breastfeeding parent’s diet) and typically resolves once the triggering protein is removed. A strep skin infection around the anus is another less obvious cause in children, sometimes producing blood-streaked stools without obvious diarrhea or illness. Bacterial gut infections can cause bloody diarrhea in kids just as they do in adults.
Signs That Require Emergency Care
Most causes of blood in the stool are not emergencies, but some are. Heavy or continuous rectal bleeding, especially when paired with severe abdominal pain or cramping, warrants an immediate trip to the emergency room.
Call 911 if rectal bleeding comes with any signs that your body is losing blood faster than it can compensate:
- Rapid, shallow breathing
- Dizziness or lightheadedness when you stand up
- Fainting or confusion
- Cold, clammy, or pale skin
- Blurred vision
- Nausea
- Very little urine output
These symptoms suggest significant blood loss and need urgent treatment. Even without those red flags, any new or unexplained rectal bleeding that persists for more than a day or two, or that keeps coming back, is worth getting evaluated. A simple exam and possibly a scope can usually identify the source and put you on the right path.