Blood in your stool is surprisingly common, affecting roughly 1 in 6 adults at some point. The cause is usually something minor like hemorrhoids or a small tear in the skin around the anus, but it can also signal conditions that need treatment. What the blood looks like, where it appears, and what other symptoms come with it all help narrow down the source.
What the Color of the Blood Tells You
The color of blood in your stool is a useful clue about where the bleeding is coming from. Bright red blood typically means the source is in the lower part of the digestive tract: the colon, rectum, or anus. The blood hasn’t had far to travel, so it stays red. You might see it on the toilet paper, in the bowl, or mixed into the stool itself.
Dark maroon or black, tarry stool points to bleeding higher up in the digestive tract, such as the stomach or upper intestine. Blood that travels through the full length of the gut gets broken down along the way, turning dark. Black, sticky stool with a distinctive strong odor is a classic sign of upper GI bleeding and is more likely to need urgent evaluation.
Before you worry, though, consider what you’ve eaten or taken recently. Beets, tomatoes, and foods with red food coloring can make stool look reddish. On the dark side, blueberries, black licorice, iron supplements, bismuth (the active ingredient in Pepto-Bismol), and activated charcoal can all turn stool black without any bleeding involved.
Hemorrhoids and Anal Fissures
These two conditions are the most frequent causes of bright red blood in the stool, and both are generally manageable. Hemorrhoids are swollen veins around the anus that can bleed during bowel movements, especially with straining. You might notice blood on the tissue or dripping into the toilet. Internal hemorrhoids are painless; external ones can itch, swell, or hurt. Anal fissures are small tears in the skin lining the anus, often caused by passing a hard or large stool. They tend to produce a sharp, burning pain during and after a bowel movement, along with a streak of bright red blood.
A doctor can usually tell the difference between the two with a simple physical exam. If the source isn’t immediately obvious, they may use an anoscope (a short, thin tube) to look just inside the anus and rectum. Both conditions often improve with dietary changes, more fiber, and staying hydrated. Most people recover without any procedures.
Diverticular Bleeding
Diverticular disease involves small pouches that form in the wall of the colon, usually in people over 40. These pouches are extremely common and usually harmless. Occasionally, though, a small blood vessel inside one of these pouches bursts. When that happens, you can pass a significant amount of blood with little or no pain, which can be alarming. The bleeding is sometimes heavy enough to require emergency care, but it often stops on its own.
This is different from diverticulitis, which is when one of those pouches becomes inflamed or infected. Diverticulitis usually causes sudden, severe pain on the lower left side of the abdomen, sometimes with fever, nausea, or changes in bowel habits. Bleeding can happen with diverticulitis too, but painless rectal bleeding without other symptoms is more characteristic of a diverticular bleed.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both involve chronic inflammation of the digestive tract, and bloody stool is one of their hallmark symptoms. In ulcerative colitis, the inflammation is concentrated in the colon and rectum, so bloody diarrhea is common. Crohn’s disease can affect any part of the GI tract and may cause blood in the stool along with abdominal pain, fatigue, and weight loss.
These conditions tend to flare and then improve in cycles. If you’re noticing blood in your stool alongside ongoing diarrhea, cramping, or unexplained weight loss over weeks or months, inflammatory bowel disease is one possibility worth investigating.
Colorectal Cancer and Polyps
This is what most people are really asking about when they search for blood in stool. Rectal cancer and colon cancer can cause bleeding, but they rarely cause bleeding as an early or only symptom. Rectal cancer often produces no symptoms at all in its early stages. When symptoms do appear, they tend to come as a cluster: a change in bowel habits that persists (new diarrhea, constipation, or feeling like your bowel doesn’t fully empty), narrower-than-usual stool, unexplained weight loss, fatigue, and abdominal pain.
One pattern worth noting: bleeding from hemorrhoids is typically bright red and occurs during or right after a bowel movement. Bleeding related to cancer can be dark or bright red and may happen at any time, not just with bowel movements. Blood that’s mixed into the stool rather than sitting on the surface is also more concerning.
Colon polyps, which are growths on the inner lining of the colon, can bleed as well. Most polyps are benign, but some can develop into cancer over time if they aren’t removed. This is why screening matters. The U.S. Preventive Services Task Force recommends colorectal cancer screening starting at age 45, continuing through age 75. The previous starting age was 50, but it was lowered because rates of colorectal cancer in younger adults have been rising.
Upper GI Bleeding
When the source of bleeding is the stomach or esophagus, the stool often appears black and tarry rather than red. The most common cause of upper GI bleeding is a peptic ulcer, which is an open sore in the stomach lining or the first part of the small intestine. Other causes include tears in the esophagus lining (sometimes from forceful vomiting), enlarged veins in the esophagus related to liver disease, and inflammation of the esophagus. Upper GI bleeding may also cause you to vomit blood or material that looks like dark coffee grounds.
Hidden Blood You Can’t See
Sometimes blood in the stool isn’t visible at all. This is called occult (hidden) blood, and it can only be detected with a lab test. A fecal occult blood test checks a stool sample for traces of blood using either a chemical reaction or an antibody that binds to blood proteins. The antibody-based version, called a FIT test, is considered more accurate. These tests are commonly used for colorectal cancer screening and can also detect bleeding from other GI conditions. If a fecal occult blood test comes back positive, the next step is usually a colonoscopy to find the source.
How Doctors Find the Source
If you report blood in your stool, the diagnostic process depends on your symptoms, age, and risk factors. A colonoscopy is the most thorough option. It uses a flexible tube with a camera to examine the entire colon and can find polyps, inflammation, diverticular disease, and tumors. A sigmoidoscopy works the same way but only views the lower portion of the colon. A CT colonography, sometimes called a virtual colonoscopy, uses imaging to create detailed pictures of the colon without a scope. If polyps or abnormal tissue are found during a colonoscopy, they can often be removed or biopsied during the same procedure.
Signs That Need Immediate Attention
Most rectal bleeding doesn’t require a trip to the emergency room, but some situations do. Seek emergency care if you’re passing a large or continuous amount of blood, or if bleeding comes with severe abdominal pain or cramping. Call 911 if you develop signs of significant blood loss: dizziness or lightheadedness when you stand up, rapid shallow breathing, blurred vision, fainting, confusion, cold or clammy skin, nausea, or very low urine output. These symptoms suggest you’re losing enough blood to affect circulation, and that needs treatment fast.
For smaller amounts of blood that you notice once or twice, especially bright red blood during a bowel movement, it’s reasonable to monitor the situation. But if it continues for more than a week or two, or if you notice any accompanying changes in your bowel habits, weight, or energy levels, getting it checked gives you a clear answer and, in most cases, real reassurance.