Blood in your stool can come from anywhere along your digestive tract, from the esophagus to the anus. The most common causes are hemorrhoids and anal fissures, both of which are generally harmless and treatable. But blood in stool can also signal conditions that need medical attention, including inflammatory bowel disease, diverticular disease, and colorectal cancer. The color and appearance of the blood often points toward where the bleeding is coming from.
What the Color of the Blood Tells You
Bright red blood in or on your stool usually means the bleeding is happening low in the digestive tract: the colon, rectum, or anus. This is the most common type people notice, often on toilet paper or in the bowl after a bowel movement. It’s frequently caused by hemorrhoids or small tears near the anus.
Dark, tarry, almost black stool (called melena) signals bleeding higher up, typically in the stomach or upper small intestine. Blood turns dark as it travels through the digestive system and gets partially digested along the way. If you’re also vomiting material that looks like dark coffee grounds, that’s another sign of upper GI bleeding. Both of these warrant prompt medical evaluation.
Maroon-colored stool falls somewhere in between and can indicate bleeding in the middle or lower portions of the small intestine or the right side of the colon.
Hemorrhoids and Anal Fissures
These two causes account for the majority of bright red rectal bleeding, especially in younger adults. Hemorrhoids are swollen veins in the rectum or anus. They can bleed during bowel movements but are often painless, particularly internal hemorrhoids. You might notice streaks of red blood on toilet paper or drops in the bowl. Straining during bowel movements, sitting for long periods, pregnancy, and chronic constipation all increase your risk.
An anal fissure is a small tear in the lining of the anal canal, usually caused by passing hard or large stools. Unlike hemorrhoids, fissures typically hurt, sometimes sharply, during and after a bowel movement. The bleeding is usually small in volume and bright red. Most fissures heal on their own within a few weeks with increased fiber intake and adequate hydration.
Diverticular Disease
Diverticula are small pouches that bulge outward through weak spots in the colon wall. They become more common with age, and most people who have them never experience problems. Occasionally, though, a blood vessel near one of these pouches can rupture and cause sudden, painless bleeding. Diverticular bleeding is one of the most common causes of significant lower GI bleeding in adults over 40. The blood is often maroon or bright red and can be heavy enough to be alarming, though it stops on its own in most cases.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract, and bloody stool is a hallmark symptom of both. In ulcerative colitis, inflammation attacks the innermost lining of the colon and rectum, creating ulcers that bleed. The result is often bloody diarrhea, sometimes mixed with mucus, along with cramping and urgency.
Crohn’s disease works differently. It can affect any part of the digestive tract and penetrates deeper into the bowel wall, through all its layers. Over time, the intestinal lining develops deep ulcerations separated by patches of normal tissue. Bleeding in Crohn’s disease is common but tends to be less dramatic than in ulcerative colitis. Both conditions are chronic and require ongoing management.
Peptic Ulcers
Peptic ulcers are open sores that form on the inner lining of the stomach or the upper part of the small intestine. They are the most common cause of upper GI bleeding. Most peptic ulcers develop from infection with a specific type of bacteria or from long-term use of pain relievers like ibuprofen and aspirin. Because the bleeding happens high in the digestive tract, the blood is usually digested by the time it reaches the stool, producing that characteristic black, tarry appearance rather than visible red blood. Burning stomach pain that worsens on an empty stomach is the classic accompanying symptom.
Colon Polyps and Colorectal Cancer
Polyps are small growths on the inner wall of the colon or rectum. Most are harmless, but some can slowly develop into cancer over years. Both polyps and colorectal cancer can cause blood in the stool, though the bleeding is often so minimal that you can’t see it with the naked eye. This is called occult (hidden) bleeding, and it’s one reason routine screening matters even when you feel fine.
The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults aged 45 to 75 who are at average risk. The fecal immunochemical test (FIT) is a simple, non-invasive stool test that detects hidden blood with 96% sensitivity for colorectal cancer and a negative predictive value of 99.8%, meaning a negative result is highly reliable. Colonoscopy remains the gold standard because it can both detect and remove polyps in the same procedure, preventing them from becoming cancerous.
Red flags that raise concern for colorectal cancer include unexplained weight loss, a persistent change in bowel habits (new constipation, narrower stools, or diarrhea lasting more than a few days), and a feeling that your bowel doesn’t fully empty. Blood in the stool alongside any of these symptoms deserves prompt evaluation.
Medications That Increase Bleeding Risk
Several common medications can either cause GI bleeding directly or make existing bleeding worse. NSAIDs like ibuprofen, naproxen, and aspirin damage the protective lining of the stomach and intestines, making ulcers and bleeding more likely. In one multicenter study, NSAID use was associated with a 2.5 times higher risk of intestinal bleeding.
Blood-thinning medications carry an even higher risk. Anticoagulants like warfarin were associated with a 4.3 times higher risk of intestinal bleeding in the same study, while antiplatelet drugs like clopidogrel carried a 3.2 times higher risk. If you take any of these medications regularly and notice blood in your stool, that’s important information to share with your doctor.
Interestingly, proton pump inhibitors (commonly taken for acid reflux) may also play a role. While they protect the stomach lining, research suggests they can alter gut bacteria in ways that increase injury to the small intestine, particularly when combined with NSAIDs.
Foods That Mimic Blood in Stool
Not everything that looks like blood actually is blood. Beets are the most well-known culprit, capable of turning stool a deep red or maroon that can be genuinely alarming. Iron supplements and bismuth-based antacids can turn stool black, mimicking the appearance of upper GI bleeding. Red meat, especially beef and lamb, can cause a positive result on certain stool tests even without any actual bleeding. If you’ve recently eaten beets or started an iron supplement and notice a color change with no other symptoms, the explanation may be dietary.
Signs of a GI Emergency
Most causes of blood in stool are not emergencies, but severe GI bleeding can become life-threatening. Large-volume bleeding, whether from a peptic ulcer, diverticular disease, or another source, can lead to shock. Warning signs include feeling confused or lightheaded, a rapid heart rate, pale skin, cold or clammy hands and feet, and heavy sweating. If you’re passing large amounts of blood, especially combined with any of these symptoms, that’s a situation requiring emergency care.
Even without dramatic bleeding, stool that is persistently black and tarry warrants urgent attention, as it can indicate steady blood loss from the upper digestive tract that adds up over time. Chronic slow bleeding sometimes shows up first as fatigue and weakness from anemia before you ever notice the stool itself looks different.