Blood in your stool is common, affecting roughly 13% to 34% of adults at some point, and the most frequent cause is hemorrhoids. That said, the color, amount, and accompanying symptoms all matter because they point to different parts of the digestive tract and different underlying conditions. Most causes are treatable and not dangerous, but a few require prompt attention.
What the Color 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 typically originates in the colon, rectum, or anus. It hasn’t traveled far, so it still looks fresh. Dark red or maroon blood has usually spent more time in the digestive tract, suggesting a source higher up in the colon or small intestine.
Black, tarry stools point to bleeding in the upper digestive tract: the esophagus, stomach, or the first section of the small intestine. Blood turns dark and sticky as it’s digested on the way down. Occasionally, very rapid bleeding from an upper source (like a stomach ulcer eroding into an artery) can produce bright red blood instead, because it moves through the system too quickly to change color.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stool look reddish. Black licorice, blueberries, iron supplements, activated charcoal, and bismuth-based antacids (like Pepto-Bismol) can all turn stool black and mimic the appearance of digested blood. If there’s any question, a simple lab test on a stool sample can confirm whether actual blood is present.
Hemorrhoids: The Most Common Cause
Hemorrhoids are the leading cause of rectal bleeding in middle-aged and older adults. Internal hemorrhoids sit inside the rectum where you can’t see or feel them, and they typically cause painless bleeding. You’ll notice small amounts of bright red blood on the toilet paper or in the bowl. Because there’s no pain, people are often caught off guard.
External hemorrhoids form under the skin around the anus and tend to itch, swell, and hurt. They can also bleed. If a blood clot forms inside one (a thrombosed hemorrhoid), you may feel a hard lump near the anus along with severe pain and swelling. Hemorrhoids develop from straining during bowel movements, sitting for long periods, pregnancy, and chronic constipation or diarrhea.
Anal Fissures
A fissure is a small tear in the lining of the anus, usually caused by passing a hard or large stool. It produces bright red blood and a sharp, stinging pain during and after a bowel movement. Fissures are extremely common and typically heal on their own within a few weeks with softer stools and good hygiene.
Diverticular Bleeding
Diverticular bleeding is one of the more dramatic causes of blood in the stool. Diverticula are small pouches that form along the colon wall, and when an artery inside one of these pouches ruptures, it can produce a large volume of blood that appears suddenly. The hallmark is painless, heavy bleeding: your abdomen won’t be tender, but the amount of blood can be alarming. Because it’s arterial, diverticular bleeding sometimes requires emergency treatment to stop, though it also stops on its own in many cases.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both fall under the umbrella of inflammatory bowel disease (IBD). These are chronic conditions in which the immune system attacks the lining of the digestive tract, causing ongoing inflammation. Blood in the stool is a core symptom, along with belly pain, cramping, and diarrhea. If you’re passing blood clots in your stool along with these symptoms, that warrants urgent medical evaluation. IBD is managed with long-term medication to control inflammation and prevent flares.
Colorectal Cancer
Cancer accounts for only about 3.4% of rectal bleeding cases, but it’s the reason doctors take blood in the stool seriously, especially in older adults. Colorectal cancer can cause subtle bleeding that you don’t even see, changes in bowel habits, unexplained weight loss, or a feeling that your bowel doesn’t fully empty. The risk increases with age and with a family history of colorectal cancer or polyps.
Current guidelines from the U.S. Preventive Services Task Force recommend that most people begin routine colorectal cancer screening soon after turning 45 and continue through age 75. Between ages 76 and 85, the decision is individual. People with higher risk factors, such as a family history, may need to start earlier. If you’ve never been screened and you’re noticing blood in your stool, that’s a reasonable time to have the conversation.
How Doctors Figure Out the Cause
Your doctor will likely start with questions: when the bleeding started, whether it’s painful or painless, what color the blood is, whether you have a history of digestive conditions, and whether colorectal cancer runs in your family. These details help narrow the possibilities quickly.
A stool test, called a fecal immunochemical test (FIT), checks for hidden blood that isn’t visible to the naked eye. It’s simple and done at home, but it has limitations. It can miss some polyps and early cancers. A colonoscopy is the most thorough option. A small camera examines the entire colon and rectum, and if the doctor spots abnormal tissue or polyps, they can remove them during the same procedure. Colonoscopy is considered one of the most sensitive screening tools available for colorectal cancer.
Signs That Need Immediate Attention
Most rectal bleeding doesn’t require a trip to the emergency room, but certain combinations of symptoms do. Heavy bleeding from the rectum paired with dizziness, confusion, rapid shallow breathing, nausea, fainting, or feeling weak suggests significant blood loss. Black or dark red stool, vomit that contains blood or looks like coffee grounds, severe rectal pain, fever, or an inability to have a bowel movement alongside heavy bleeding are also reasons to seek emergency care right away.
A small streak of bright red blood on the toilet paper after a hard bowel movement is a very different situation from passing large amounts of dark blood with abdominal pain. The former is likely a hemorrhoid or fissure. The latter could indicate something that needs treatment within hours. Paying attention to the full picture, not just the blood itself, helps you gauge how urgently to act.