Blood in your stool usually signals that something is bleeding somewhere along your digestive tract. The cause can range from something minor and common, like hemorrhoids, to something that needs prompt medical attention, like an ulcer or inflammatory bowel disease. What the blood looks like, where it appears, and what other symptoms accompany it all help narrow down what’s going on.
What the Color of the Blood Tells You
The color of blood in your stool is one of the most useful clues to its source, because blood changes color the longer it travels through your digestive system. Hemoglobin, the protein that makes blood red, gets progressively darker as digestive enzymes break it down. That means the color roughly maps to where the bleeding is happening.
Bright red blood on the toilet paper, in the bowl, or coating the surface of your stool points to bleeding in the lower digestive tract: the rectum, anus, or lower colon. This is the most common presentation and is often caused by hemorrhoids or small tears near the anus.
Dark red or maroon blood mixed into the stool suggests bleeding higher up in the colon or in the small intestine. Black, tarry stools with a distinct sticky texture and strong odor indicate bleeding even higher, typically in the stomach or upper small intestine. By the time blood from the stomach reaches the other end, enzymes have broken it down enough to turn it black.
Foods and Medications That Mimic Blood
Before assuming the worst, it’s worth knowing that certain foods and supplements can change stool color in ways that look alarming. Beets and foods with red coloring can make stool appear reddish. Black licorice, blueberries, iron supplements, 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 what you’re seeing. The difference is that these color changes are usually uniform and don’t come with other symptoms like pain or dizziness.
The Most Common Causes
Hemorrhoids and anal fissures are by far the most frequent reasons people notice blood after a bowel movement. Both produce bright red blood that you might spot on the toilet paper, in the toilet, or on the stool itself. Both can cause pain that worsens during bowel movements, along with itching around the anus. The key difference: hemorrhoids can create a feeling of incomplete emptying, as if you still need to go when you don’t. Internal hemorrhoids often don’t cause pain at all unless they’ve started to protrude. Anal fissures, which are small tears in the lining of the anus, tend to cause a sharper, more focused pain.
These conditions are common in people who strain during bowel movements, sit for long periods, deal with chronic constipation or diarrhea, or are pregnant. They often resolve on their own or with simple changes like increasing fiber and water intake.
Digestive Conditions That Cause Bleeding
Several conditions affecting the colon and intestines can produce blood in the stool, and they tend to come with additional symptoms beyond just bleeding.
Diverticulosis involves the development of small, bulging pouches in the wall of the digestive tract. These pouches are common as people age and usually cause no problems at all. But when a blood vessel near one of these pouches breaks, it can cause sudden, painless bleeding that ranges from minor to significant. Diverticular bleeding often stops on its own, but heavy or recurring episodes need medical evaluation.
Ulcerative colitis causes swelling and sores in the colon and rectum. Bloody diarrhea is one of its hallmark symptoms, often accompanied by cramping, urgency, and fatigue. Crohn’s disease involves similar inflammation but can affect any part of the digestive tract lining. Both are forms of inflammatory bowel disease and tend to flare and remit over time.
Peptic Ulcers
Ulcers in the stomach or upper small intestine are a common cause of black, tarry stools. Because the bleeding happens high in the digestive tract, the blood is fully broken down by the time it exits. Two things cause most peptic ulcers: infection with a specific type of bacteria and regular use of common pain relievers like aspirin, ibuprofen, and naproxen. These medications relieve pain effectively, but they also make the stomach lining more vulnerable to damage. Your risk goes up if you take these pain relievers for a long time, at high doses, or in combination with each other.
Colorectal Cancer and Polyps
Blood in the stool can be a sign of colorectal cancer or precancerous polyps, which is one reason this symptom gets people’s attention. Polyps are growths on the inner lining of the colon that can bleed intermittently, sometimes in amounts too small to see with the naked eye. When cancer is the cause, bleeding may be accompanied by changes in bowel habits, unexplained weight loss, persistent cramping, or a feeling that the bowel doesn’t empty completely.
Colorectal cancer screening is recommended for all average-risk adults starting at age 45 and continuing through age 75, according to the U.S. Preventive Services Task Force. “Average risk” means no prior history of polyps, inflammatory bowel disease, or genetic conditions like Lynch syndrome that raise lifetime cancer risk. For adults 76 to 85, screening decisions are more individualized based on overall health and prior screening history. If you’re under 45 and notice persistent blood in your stool, that’s still worth investigating, especially if you have other symptoms or a family history of colorectal cancer.
How Doctors Figure Out the Source
The diagnostic process depends on what your doctor suspects based on your symptoms, age, and medical history. A physical exam and questions about what the blood looks like, how often it appears, and what other symptoms you have will guide next steps.
A fecal immunochemical test (FIT) checks for hidden blood in a stool sample you collect at home. It’s convenient and noninvasive, but it has real limitations. Its ability to detect precancerous growths is modest, catching roughly one in four advanced cases. A negative result doesn’t rule everything out.
A colonoscopy provides a direct visual inspection of the entire colon and allows doctors to remove polyps or take tissue samples during the same procedure. It’s the most thorough option for evaluating lower digestive tract bleeding. For suspected upper digestive tract bleeding (the kind that produces black, tarry stools), a similar scope examination of the stomach and upper intestine is used instead.
Signs That Need Immediate Attention
A small amount of bright red blood on the toilet paper after a hard bowel movement is common and often not an emergency. But heavy bleeding or blood accompanied by systemic symptoms is a different situation. Seek emergency care if rectal bleeding comes with any of these signs:
- Rapid, shallow breathing
- Dizziness or lightheadedness when standing up
- Blurred vision or fainting
- Confusion or nausea
- Cold, clammy, pale skin
- Very low urine output
These are signs the body is losing enough blood to affect circulation. Black, tarry stools also warrant a prompt call to your doctor, since they point to active bleeding in the upper digestive tract that you can’t see directly. Even without dramatic symptoms, blood in the stool that persists for more than a day or two, recurs regularly, or shows up alongside weight loss or changes in bowel habits deserves medical evaluation rather than a wait-and-see approach.