Blood in your stool is common and usually not dangerous, but it always deserves attention. Roughly one in seven adults has experienced rectal bleeding at some point, and the cause is often something minor like hemorrhoids or a small tear. Still, blood in your stool can occasionally signal something more serious, so understanding what different types of bleeding look like and when to act is important.
What the Color of the Blood Tells You
The color of the blood is the single most useful clue about where the bleeding is coming from. Bright red blood typically means the source is in the lower part of your digestive tract: the colon, rectum, or anus. Dark red or maroon blood often points to bleeding higher up in the colon or small intestine. Black, tarry stool that looks like coffee grounds usually means bleeding in the stomach or esophagus, because blood darkens and changes texture as it travels through the full length of your digestive system.
Before assuming the worst, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stool look reddish. Iron supplements, black licorice, blueberries, activated charcoal, and bismuth-based medications like Pepto-Bismol can all turn stool black. If you’ve consumed any of these in the past day or two, that may explain the color change entirely.
Common Causes of Bright Red Blood
Hemorrhoids are the most common cause of blood in stool. These are swollen veins in the rectum or anus, and they usually develop from straining during bowel movements, sitting for long periods, constipation, pregnancy, or obesity. Most hemorrhoids don’t cause pain. You might notice blood on the toilet paper, in the bowl, or coating the stool itself.
Anal fissures are small tears in the lining of the anal canal, often from passing hard or large stools. Unlike hemorrhoids, fissures tend to hurt, sometimes sharply, especially during a bowel movement. You’ll typically see blood when you wipe. Both hemorrhoids and fissures are more about discomfort than danger, and most resolve on their own or with simple changes like adding fiber and drinking more water.
Diverticulitis is another possibility. Small pouches can form in the colon wall over time, and when these become infected or inflamed, the blood vessels inside them can rupture. This can produce noticeable bleeding that’s sudden and painless, sometimes filling the toilet bowl with bright or dark red blood. Diverticular bleeding often stops on its own but can be heavy enough to need medical evaluation.
Causes of Dark or Black Stool
When stool is black and sticky (sometimes described as looking like tar), the bleeding source is usually in the stomach, esophagus, or the first section of the small intestine. The most common cause is a peptic ulcer, which is an open sore in the stomach lining or upper intestine. Severe inflammation of the stomach lining (from alcohol, certain medications, or infection) can also produce this kind of bleeding.
Less common but more serious causes include swollen veins in the esophagus that rupture, often related to liver disease, or a tear in the esophagus from violent vomiting. Cancers of the stomach, esophagus, or pancreas can also cause dark stool, though these are far less frequent than ulcers or inflammation.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract, and blood in the stool is a hallmark symptom of both. The bleeding in these conditions typically comes with other persistent symptoms: ongoing diarrhea, abdominal pain, extreme fatigue, and unintentional weight loss. If you’re seeing blood alongside these patterns over weeks or months rather than as a one-time event, inflammatory bowel disease is worth investigating.
Colorectal Cancer
This is what most people are really worried about when they search this topic. Colorectal cancer is the third most commonly diagnosed cancer in the United States and can cause blood in the stool, but it’s far from the most likely explanation. The blood may be visible or invisible to the naked eye, and it’s often accompanied by changes in bowel habits, unexplained weight loss, a feeling that the bowel doesn’t fully empty, or persistent cramping.
The U.S. Preventive Services Task Force recommends that all adults begin colorectal cancer screening at age 45 and continue through age 75. For people at average risk, a colonoscopy every 10 years is one option. Less invasive alternatives include a yearly stool test (called a FIT) that detects hidden blood, or a stool DNA test every three years. If you’re over 45 and haven’t been screened, blood in your stool is a good reason to start.
Signs That Need Immediate Attention
Most rectal bleeding isn’t an emergency, but certain combinations of symptoms change the picture. If you’re seeing blood in your stool along with any of the following, seek medical help right away:
- Lightheadedness, dizziness, or fainting
- Severe abdominal cramps or pain
- Shortness of breath or unusual fatigue
- Rapid heart rate, pale skin, cold hands and feet, or heavy sweating
That last cluster of symptoms can indicate shock from significant blood loss, which is life-threatening and requires emergency care. Confusion or loss of consciousness with bleeding is also a 911 situation.
How Doctors Find the Source
If you bring up blood in your stool, a doctor will typically start with questions about the color, frequency, and any accompanying symptoms. From there, testing might include a stool sample to check for hidden blood that isn’t visible, especially if the bleeding is intermittent or subtle.
For a closer look, the standard tool is an endoscopy, where a thin, flexible tube with a camera is guided through part of the digestive tract. An upper endoscopy examines the esophagus, stomach, and upper small intestine. A colonoscopy examines the rectum and entire colon. During either procedure, the doctor can take small tissue samples for testing and, in some cases, treat active bleeding on the spot. The type of test depends on where the doctor suspects the bleeding is coming from based on the color of blood and your other symptoms.
What to Pay Attention To
A single episode of bright red blood on the toilet paper after a hard bowel movement, with no other symptoms, is most likely a hemorrhoid or fissure. It’s worth mentioning at your next doctor’s visit but rarely requires urgent action. What matters more is the pattern. Bleeding that recurs over weeks, changes in your usual bowel habits, blood mixed into the stool rather than just on the surface, dark or tarry stool, or any of the red-flag symptoms above all warrant a prompt call to your doctor. The cause is usually treatable, and catching serious conditions early makes a significant difference in outcomes.