Blood in stool is common, and in most cases it comes from something minor like hemorrhoids or a small tear near the anus. But it can also signal something more serious, so knowing what to look for and when to act matters. The first step is figuring out whether what you’re seeing is actually blood, since several foods and medications can mimic its appearance.
What Blood in Stool Actually Looks Like
Blood in stool doesn’t always look the same. Its color depends on where the bleeding is happening in your digestive tract, and that distinction gives you and your doctor important information.
Bright red blood, whether on the toilet paper, in the bowl, or coating the stool, typically comes from the lower digestive tract: the rectum, anus, or lower colon. This is the most common type people notice, and it’s often caused by hemorrhoids or anal fissures.
Maroon or dark red blood mixed into the stool usually points to bleeding higher up in the colon. This can come from inflamed pouches in the colon wall, polyps, or inflammatory bowel disease.
Black, tarry stools suggest bleeding even higher in the digestive tract, such as the stomach or upper small intestine. The blood turns dark because it gets broken down by digestive enzymes as it travels through. These stools often have a distinctive sticky texture and strong odor. Black tarry stools generally warrant prompt medical attention because they indicate upper gastrointestinal bleeding.
Foods and Medications That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stools appear reddish, closely mimicking the look of blood. On the darker end, black licorice, blueberries, iron supplements, activated charcoal, and bismuth-containing medications (the active ingredient in Pepto-Bismol) can all turn stools black. If you’ve consumed any of these in the last day or two, that may explain what you’re seeing. The easiest way to check is to stop eating the suspect food and see if your stool returns to its normal color within a couple of days.
The Most Common Causes
Hemorrhoids are the most common cause of blood in stool. These are swollen veins in the rectum or anus that often develop from straining during bowel movements, sitting for long periods, or constipation. The bleeding is usually painless and shows up as bright red streaks on toilet paper or in the bowl.
Anal fissures, small tears in the lining of the anal canal, are the second most frequent culprit. Unlike hemorrhoids, fissures tend to cause sharp pain during and after a bowel movement along with the bleeding. They’re also commonly triggered by straining or passing hard stools.
Beyond these two, the list of possible causes gets broader:
- Inflammatory bowel disease (IBD): Conditions like Crohn’s disease and ulcerative colitis cause chronic inflammation in the intestinal lining, which can lead to bloody diarrhea, cramping, and weight loss.
- Diverticulosis: Small pouches that form in the colon wall can occasionally rupture a blood vessel, causing sudden, painless bleeding that’s sometimes heavy.
- Colon polyps: These growths on the inner lining of the colon are usually harmless but can bleed and, over time, some may develop into cancer.
- Infections: Bacterial infections from organisms like E. coli or C. difficile can inflame the colon and cause bloody diarrhea, often accompanied by fever and cramping.
- Colorectal cancer: Persistent bleeding, especially with unexplained weight loss, changes in bowel habits, or narrowing of stools, can be a sign of cancer in the colon or rectum.
In one study of patients referred for colonoscopy after reporting rectal bleeding, about 55% had benign causes like hemorrhoids or diverticular disease, while roughly 44% had more significant findings including polyps, inflammatory bowel disease, or cancer. That’s not meant to alarm you. People referred for colonoscopy are already a selected group, and the vast majority of rectal bleeding in the general population comes from minor causes. But it does illustrate why persistent or unexplained bleeding is worth investigating.
Hidden Blood You Can’t See
Sometimes blood in stool isn’t visible at all. This is called occult (hidden) blood, and it can only be detected through testing. A fecal immunochemical test, or FIT, is the most common screening tool. You collect a small stool sample at home and send it to a lab, where it’s checked for trace amounts of blood. FIT detects 70% to 82% of significant colorectal issues on a single test, and its accuracy improves with annual testing. Your doctor may recommend this as part of routine colorectal cancer screening, which is now recommended for all adults starting at age 45 and continuing through age 75.
What to Track Before Calling Your Doctor
If you notice blood in your stool and it’s not an emergency, paying attention to a few details will help your doctor figure out the cause more quickly. Note the color of the blood (bright red, dark, or black), whether it’s on the surface of the stool, mixed in, or only on the toilet paper, and how often it’s happening. Also track any changes in your bowel habits, such as new diarrhea or constipation, and whether you’re experiencing pain, cramping, or straining.
A single episode of bright red blood on toilet paper after a hard bowel movement is almost always a hemorrhoid or fissure and often resolves on its own with more fiber and water. Bleeding that recurs over several days, or that you can’t easily explain, deserves a call to your doctor even if it seems minor.
When Rectal Bleeding Is an Emergency
Most rectal bleeding is not an emergency, but certain situations require immediate medical attention. Seek emergency care if bleeding is continuous or heavy, or if it’s accompanied by severe abdominal pain or cramping.
Call 911 if you’re experiencing signs of significant blood loss alongside the bleeding: rapid or shallow breathing, dizziness or lightheadedness when standing, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These are signs your body isn’t circulating enough blood, and they require urgent treatment regardless of what’s causing the bleeding.