Blood in your stool usually comes from somewhere along your digestive tract, and the cause ranges from something minor like hemorrhoids to something that needs prompt medical attention. The color of the blood is your first clue: bright red typically means the bleeding is near the end of the digestive tract (colon, rectum, or anus), while black, tarry stool points to bleeding higher up, in the stomach or upper small intestine.
What the Color Tells You
Bright red blood on the toilet paper, in the bowl, or mixed into your stool means the source is usually in the lower digestive tract. The blood hasn’t had time to be broken down, so it looks fresh. This is the most common type people notice, and hemorrhoids are the single most frequent explanation.
Black, tarry, unusually sticky stool with a strong odor is a different signal. Digestive chemicals interact with blood as it travels from the stomach or upper small intestine, changing its color and texture along the way. The longer the blood has been in transit, the darker and smellier it becomes. This type of bleeding can come from stomach ulcers, erosion of the stomach lining, ruptured veins in the esophagus, or, less commonly, cancers of the stomach, esophagus, or pancreas.
Dark maroon stool falls somewhere in between and can indicate bleeding in 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 otherwise healthy adults. Hemorrhoids are swollen blood vessels in or around the anus. Most hemorrhoids don’t cause pain. You’ll typically notice small amounts of bright red blood on the toilet paper or dripping into the bowl after a bowel movement, sometimes with mild discomfort or itching.
Anal fissures are small tears in the skin lining the anus, often caused by passing hard or large stools. They’re more likely to cause sharp pain during and after a bowel movement compared to hemorrhoids. The bleeding pattern looks similar (bright red, usually on the surface of the stool or on the paper), but the pain is the distinguishing feature. Most fissures heal on their own within a few weeks with increased fiber and water intake.
Infections That Cause Bloody Stool
Certain bacterial infections cause bloody diarrhea that comes on suddenly, often with cramping, fever, and nausea. The most common culprits in developed countries are Campylobacter, Salmonella, Shigella, and a strain of E. coli called O157:H7. That last one is particularly concerning because it can trigger a serious complication affecting the kidneys and blood cells, especially in young children and older adults.
These infections usually come from contaminated food or water. Most cases resolve within a week, but bloody diarrhea paired with high fever or signs of dehydration warrants a stool culture to identify the specific bacteria involved.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both involve chronic inflammation of the digestive tract, but they cause bleeding in different patterns. In both conditions, the immune system becomes overactive and sends white blood cells into the lining of the digestive tract, where they release inflammatory chemicals that damage tissue and cause pain, diarrhea, and bleeding.
Ulcerative colitis almost always involves the rectum and colon, so bloody diarrhea is one of its hallmark symptoms. You might also feel a sudden, urgent need to use the bathroom and a persistent sensation that your bowels haven’t fully emptied. Cramps and bleeding tend to center in the lower abdomen.
Crohn’s disease can affect any part of the digestive tract, including the small intestine, so it often shows up as abdominal pain with diarrhea that isn’t bloody, along with unintended weight loss. When Crohn’s does involve the colon, though, bleeding can occur. If you’re experiencing recurring episodes of bloody stool alongside persistent abdominal pain, fatigue, or weight loss, these conditions are worth investigating.
Colorectal Cancer
Rectal bleeding is one possible symptom of colorectal cancer, though it’s far from the most common cause of blood in your stool. What makes colorectal cancer worth mentioning is that it rarely causes bleeding alone. It tends to show up alongside other changes: a shift in your bowel habits (new constipation, diarrhea, or more frequent trips to the bathroom), stools that become noticeably narrow, a feeling that your bowel doesn’t fully empty, unexplained weight loss, persistent fatigue, or abdominal pain.
The U.S. Preventive Services Task Force recommends colorectal cancer screening for all average-risk adults starting at age 45. A colonoscopy every 10 years is one option, and it has the longest interval between screenings when results are negative. Stool-based tests are another option. The fecal immunochemical test (FIT) detects about 76% of colorectal cancers in a single round of testing, compared to roughly 39% for the older guaiac-based test, making FIT the preferred stool screening method.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Several common foods and medications can make your stool look alarmingly red or black without any actual bleeding.
- Red-colored stool mimics: beets, red gelatin, red fruit punch, red licorice, and red-dyed snack foods (like spicy “red hot” chips)
- Black-colored stool mimics: iron supplements, bismuth-containing stomach medicines (like Pepto-Bismol), activated charcoal, blueberries, chocolate, and large amounts of dark leafy greens like spinach or kale
If you recently ate beets and notice reddish stool a day or two later, that’s almost certainly the explanation. The discoloration from foods and supplements is harmless and clears up once they pass through your system.
Upper Digestive Tract Bleeding
Bleeding from the stomach or upper small intestine usually shows up as black, tarry stool rather than bright red blood. Peptic ulcers, which are open sores in the stomach lining or the first part of the small intestine, are the most common cause. Erosion of the stomach lining from prolonged use of anti-inflammatory painkillers or heavy alcohol consumption can also trigger it, as can tears in the esophagus caused by violent vomiting.
Occasionally, upper digestive tract bleeding is heavy enough that blood moves through the intestines quickly and comes out bright red. This is less common but represents a more urgent situation because of the volume of blood loss involved.
Signs That Need Immediate Attention
A small amount of bright red blood on the toilet paper after straining is common and often not an emergency. But certain combinations of symptoms signal significant blood loss that requires immediate care:
- Heavy or continuous bleeding that doesn’t stop
- Dizziness or lightheadedness when you stand up
- Rapid, shallow breathing
- Cold, clammy, or pale skin
- Confusion or fainting
- Severe abdominal pain or cramping alongside the bleeding
- Blurred vision or nausea
These are signs of shock from blood loss and warrant calling emergency services. Rectal bleeding that is continuous, heavy, or paired with severe abdominal pain also calls for an emergency room visit, even if you feel otherwise stable. For smaller amounts of bleeding that recur over days or weeks, scheduling an appointment with your doctor is the right next step to identify the source and rule out anything serious.