Blood in your stool is common, and in most cases it comes from a minor, treatable cause like hemorrhoids or a small tear in the skin around the anus. But the color, amount, and accompanying symptoms all matter, because rectal bleeding can also signal conditions that need prompt medical attention. Understanding what different types of bleeding look like, and what your body is telling you, helps you figure out your next step.
What the Color of the Blood Tells You
The single most useful clue is whether the blood is bright red or dark and tarry. Bright red blood on the toilet paper, in the bowl, or coating the stool typically comes from the lower digestive tract: the colon, rectum, or anus. Dark, tarry, almost black stool points to bleeding higher up, usually in the stomach or upper small intestine. Digestive chemicals break down the blood as it travels through the gut, changing its color and giving it a distinct, unusually foul smell. The longer the blood has been in your system, the darker and stickier it becomes.
Bright red blood that drips into the toilet or shows up only when you wipe is the most common presentation, and it’s the one most often linked to minor causes. A large volume of dark or tarry stool is a more urgent sign, because it suggests a source of bleeding you can’t see and that may have been going on for some time.
The Most Common (and Least Serious) Causes
Hemorrhoids are by far the leading reason people notice blood after a bowel movement. About half of all adults will develop a hemorrhoid by age 50. They’re swollen blood vessels in or around the rectum, and most of them don’t cause pain. You might see small amounts of bright red blood on the tissue or in the bowl, sometimes with mild discomfort or itching.
Anal fissures are the other frequent culprit. These are tiny tears in the skin lining the anus, often caused by passing hard or large stools. Unlike hemorrhoids, fissures tend to hurt, especially during a bowel movement. You’ll typically notice a small streak of blood on the stool or on the paper. Infants and adults over 50 are most prone to fissures, but anyone can get one after a bout of constipation or diarrhea.
Both conditions generally improve with dietary fiber, adequate water, and avoiding straining. If the bleeding is small, painless, and happens only occasionally, one of these two causes is the most likely explanation.
Diverticular Bleeding
In adults over 60, small pouches called diverticula that form along the colon wall are a major source of lower GI bleeding. In one study, diverticular bleeding accounted for nearly 59% of all acute lower intestinal bleeding cases, with the average patient age around 70. About 17% of those patients were younger than 60, so it’s not exclusively a condition of older adults.
Diverticular bleeding often starts suddenly and can be heavy, producing a noticeable amount of dark red or maroon blood. It usually stops on its own, but the volume of blood can be alarming enough to warrant a trip to the emergency room. If you’re over 50 and experience a sudden, painless gush of blood from the rectum, this is one of the first things a doctor will consider.
When Blood in Your Stool Could Be Something More Serious
Colorectal cancer and inflammatory bowel disease (conditions like Crohn’s disease and ulcerative colitis) can both cause rectal bleeding, which is why persistent or unexplained blood in your stool should never be written off as “just hemorrhoids” without confirmation.
Colon cancer often produces no symptoms in its early stages. When symptoms do appear, they typically include a combination of changes: a shift in your usual bowel habits (more diarrhea or constipation than normal), ongoing belly cramps or gas, a feeling that your bowel isn’t fully emptying, unexplained weight loss, or persistent fatigue. Blood in the stool may be visible, or it may be present only in microscopic amounts you can’t see. The key distinction is that bleeding from cancer or IBD rarely occurs in isolation. It almost always comes with other symptoms that develop gradually over weeks or months.
The U.S. Preventive Services Task Force recommends that all average-risk adults begin colorectal cancer screening at age 45, with routine screening continuing through age 75. “Average risk” means no personal or family history of colorectal cancer, polyps, or inflammatory bowel disease. If you have those risk factors, screening should start earlier.
Dark or Tarry Stools and Upper GI Bleeding
Black, sticky, tar-like stools are a hallmark of bleeding in the stomach or upper small intestine. The most common cause is a peptic ulcer, which is an open sore in the lining of the stomach or the first part of the small intestine. Regular use of common over-the-counter pain relievers like ibuprofen, aspirin, and naproxen increases your risk of developing these ulcers significantly.
Because the blood has traveled the full length of the digestive tract, it looks nothing like fresh blood. It’s black, has a tar-like consistency, and carries a strong, distinctive odor. If you notice stools that fit this description and you haven’t recently taken iron supplements or bismuth-containing products (like Pepto-Bismol), it warrants prompt medical evaluation.
Foods and Medications That Mimic Blood
Before panicking, consider what you’ve eaten or taken recently. Several common substances can change your stool color in ways that look like bleeding but are completely harmless.
- Black stools: Iron supplements, activated charcoal, and bismuth-based antacids (Pepto-Bismol, Kaopectate) all turn stools black. This is a chemical reaction, not blood.
- Red or reddish stools: Beets, red gelatin, tomato soup, and red food dyes can all produce startlingly red stools. Certain medications, including rifampin and some antacids containing aluminum, can do the same.
- Reddish stools in infants: A common antibiotic (cefdinir) can react with the iron in baby formula to produce alarming red-colored stools that contain no blood at all.
If you suspect a food or supplement is responsible, stopping it for two to three days should return your stool to its normal color. If the color persists after that, something else is going on.
Signs You Need Emergency Care
Most rectal bleeding does not require an ambulance, but some situations do. Call 911 or get to an emergency room if you experience significant bleeding along with any signs that your body isn’t handling the blood loss well: rapid or shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These are signs of shock, meaning your blood volume has dropped enough to affect your organs.
You should also seek immediate care if the bleeding is continuous or heavy (not just a few drops), or if it’s accompanied by severe abdominal pain or cramping. Heavy bleeding means you’re filling the toilet bowl with blood, passing large clots, or soaking through clothing.
What Happens When You Get It Checked Out
For most people, an evaluation starts with a physical exam and a conversation about your symptoms, diet, and medications. Your doctor may perform a visual inspection of the anal area or a brief internal exam to check for hemorrhoids or fissures.
If the cause isn’t immediately obvious, the next step is often a stool test that checks for hidden blood, or a colonoscopy, which is a camera exam of the full colon. A colonoscopy lets the doctor see the lining of the colon directly and take small tissue samples if anything looks unusual. It’s the most thorough way to rule out polyps, cancer, and inflammatory conditions. The preparation (clearing out your bowel the day before) is the most unpleasant part; the procedure itself is done under sedation, and most people don’t remember it.
If your doctor suspects upper GI bleeding based on dark stools, an upper endoscopy, which uses a similar camera passed through the mouth into the stomach, is the standard next step.