Blood in your stool usually comes from something treatable and non-dangerous, like hemorrhoids or a small tear in the skin around the anus. But it can also signal conditions that need medical attention, from inflammatory bowel disease to colon polyps. The color, amount, and accompanying symptoms all help narrow down the cause.
What the Color of the Blood Tells You
The color of blood in your stool is the single most useful clue about where the bleeding is coming from. Bright red blood on the toilet paper or coating the stool typically points to a source near the end of the digestive tract: the rectum, anus, or lower colon. The blood hasn’t had time to be broken down, so it still looks red.
Dark, tarry, almost black stool points to bleeding higher up, in the stomach or upper small intestine. As blood travels through the digestive tract, stomach acid transforms it from red to a dark, sticky substance that looks like tar and has a distinctive foul smell. It takes roughly 100 to 200 mL of blood in the upper GI tract to produce this kind of stool, and the dark color can persist for several days after the bleeding has actually stopped.
Maroon-colored stool falls somewhere in between and often suggests bleeding in the right side of the colon or the small intestine. Occasionally, a very brisk bleed from the stomach or upper intestine moves through so quickly that it comes out bright red rather than black, which can be misleading.
Hemorrhoids and Anal Fissures
These two conditions are the most common reasons people see bright red blood after a bowel movement, and they feel quite different from each other. Hemorrhoids, especially internal ones, tend to cause painless bleeding. You might notice blood on the tissue, dripping into the bowl, or even small clots. External hemorrhoids often appear as soft lumps around the anus and are more likely to itch or produce a dull ache than sharp pain.
Anal fissures are tiny tears in the lining of the anus, usually caused by passing hard stool. They produce smaller amounts of bright red blood but come with a sharp, burning pain that can last for hours after you finish. Itching is uncommon with fissures. If your main symptom is itching with some bleeding, hemorrhoids are the more likely culprit. If it’s a stinging, burning pain concentrated right at the opening, a fissure is more probable.
Diverticular Bleeding
Diverticulosis, where small pouches form in the colon wall, is extremely common in adults over 50. Most people with these pouches never have problems, but 10 to 15% will experience bleeding at some point. Diverticular bleeding is actually the most common cause of significant lower GI bleeding in adults, responsible for up to half of all cases.
What makes diverticular bleeding distinctive is the combination of volume and painlessness. Because the bleeding comes from a small artery inside the pouch, it tends to be moderate to heavy, producing fresh red or maroon-colored stool, but it typically happens without any abdominal pain. This sets it apart from most other causes, where pain or cramping usually accompanies the blood. Most episodes stop on their own, but the risk of a repeat bleed is high: up to 47% within eight months of the first episode.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both involve chronic inflammation of the digestive tract, and both can cause blood in the stool, though the pattern differs. Ulcerative colitis is the more likely culprit when blood is a prominent symptom. It typically causes bloody diarrhea, sudden urgent trips to the bathroom, and the frustrating sensation of still needing to go even after you’ve finished. Because the inflammation starts in the rectum and extends upward through the colon, cramping and bleeding tend to center in the lower abdomen.
Crohn’s disease more often involves abdominal pain with nonbloody diarrhea and unintended weight loss, particularly when the small intestine is affected. Blood in the stool is possible with Crohn’s but less consistently present than with ulcerative colitis. Either condition tends to follow a pattern of flares and remissions, so symptoms that come and go over weeks or months are worth paying attention to.
Foods and Medications That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets, red gelatin, tomato soup, and foods with red dye can turn stool reddish enough to look alarming. On the dark end, iron supplements, bismuth-containing antacids like Pepto-Bismol, activated charcoal, black licorice, and blueberries can all produce stool dark enough to be mistaken for the tarry black of upper GI bleeding. If you’ve consumed any of these in the past day or two, that’s likely your explanation. The easiest test: stop the suspect food or supplement and see if the color returns to normal within a couple of days.
Colon Polyps and Colorectal Cancer
This is the possibility most people are worried about when they search this question. Colon polyps, which are small growths on the inner lining of the colon, can bleed intermittently and are often the precursors to colorectal cancer. The bleeding from polyps or early-stage cancer is frequently too small to see with the naked eye, which is why screening tests exist to detect hidden (occult) blood.
The U.S. Preventive Services Task Force recommends that all adults at average risk begin colorectal cancer screening at age 45 and continue through age 75. This applies to people with no prior history of polyps, inflammatory bowel disease, or genetic conditions like Lynch syndrome that raise colorectal cancer risk. If you have those risk factors, screening starts earlier.
One common screening option is the fecal immunochemical test (FIT), a stool test you can do at home. FIT detects about 76% of colorectal cancers when everyone in the study also gets a colonoscopy for comparison, and up to 89% in real-world screening conditions where only positive results are followed up with colonoscopy. An older version of this test, called the guaiac-based fecal occult blood test, catches significantly fewer cancers (around 39 to 59%). If your doctor offers you a choice, FIT is the more accurate stool-based option.
Signs That Bleeding Is an Emergency
Most rectal bleeding is not an emergency, but heavy or rapid blood loss from anywhere in the GI tract can become dangerous. The body’s response to significant blood loss is shock, and the warning signs are unmistakable: confusion or loss of consciousness, a racing heart, pale skin, cold or clammy hands and feet, and heavy sweating. Any combination of these symptoms with visible blood in your stool or vomit warrants immediate emergency care.
Vomiting blood is another red flag. Bright red blood in vomit points to active upper GI bleeding, while vomit that looks like dark coffee grounds suggests bleeding that has slowed, with the blood partially digested by stomach acid. Either presentation needs urgent evaluation.
Even without dramatic symptoms, some patterns deserve prompt attention: persistent bleeding over several days, blood mixed into the stool rather than just on the surface, unexplained weight loss, changes in bowel habits lasting more than a few weeks, or new bleeding in someone over 45 who hasn’t been screened for colorectal cancer. A single episode of bright red blood on the toilet paper after straining is rarely cause for alarm, but recurring or unexplained bleeding is your body telling you something worth investigating.