Blood in your stool usually comes from somewhere in your digestive tract, and the cause ranges from something minor like hemorrhoids to something that needs prompt medical attention. Community-based studies estimate that 13% to 34% of adults experience rectal bleeding at some point, making it one of the most common gastrointestinal symptoms. Most of the time, the cause is not serious, but the color, amount, and accompanying symptoms all matter in figuring out what’s going on.
What the Color of the Blood Tells You
The color of blood in your stool is a rough map of where the bleeding is coming from. Bright red blood typically originates in the lower part of your digestive tract: the colon, rectum, or anus. This is the most common type people notice, often on toilet paper or dripping into the bowl after a bowel movement.
Black, tarry stools signal bleeding higher up, usually in the stomach or the first section of the small intestine. Blood turns black as it travels through the digestive system and gets broken down by stomach acid and enzymes. This type of stool often has a sticky consistency and a distinctly foul smell that’s different from normal stool odor. Black tarry stools generally warrant quicker medical evaluation because upper GI bleeding can involve significant blood loss before you realize it.
Before you panic, though, certain foods and supplements can mimic bloody stool. Iron pills, bismuth medications (like Pepto-Bismol), activated charcoal, black licorice, and blueberries can all turn stool black. Beets and red food coloring can make stool look reddish. A simple chemical test at your doctor’s office 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, which sit inside the rectum, cause painless bleeding. You’ll typically see bright red blood as streaks on toilet paper, on the surface of the stool, or dripping into the toilet bowl after a bowel movement. There’s usually no pain with internal hemorrhoids unless they prolapse (push out through the anus).
External hemorrhoids, which develop under the skin around the anus, are more likely to cause a noticeable lump, itching, and discomfort. They can bleed too, especially if a blood clot forms inside them.
Anal Fissures: Bleeding With Pain
An anal fissure is a small tear in the lining of the anal canal, most often caused by passing hard stools during constipation or during childbirth. The key difference from hemorrhoids is pain. Fissures typically cause sharp pain during a bowel movement, sometimes followed by a throbbing ache that lasts for hours afterward. You’ll see blood on toilet tissue or on the surface of the stool, similar to hemorrhoids, but the pain is the distinguishing feature. Most fissures heal on their own with increased fiber intake and hydration to soften stools.
Diverticular Bleeding
Diverticular bleeding is actually the most common cause of significant lower GI bleeding, meaning larger volumes of blood rather than just streaks on toilet paper. Diverticula are small pouches that form in the colon wall, and over time the blood vessels within them become fragile and prone to rupture.
The good news is that 70% to 80% of diverticular bleeding episodes stop on their own without treatment. The concerning part is that rebleeding occurs in up to 38% of patients, with about 28% experiencing another episode within two years. Risk increases substantially with age. In one hospital study, 77% of patients over 80 developed bleeding from their diverticula, compared to only 4% of younger patients. Regular use of common pain relievers like ibuprofen, blood thinners, and certain blood pressure medications also raises the risk.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease can both cause rectal bleeding, though they look different. Ulcerative colitis, which affects the colon and always involves the rectum, commonly causes bloody diarrhea along with urgent, frequent trips to the bathroom and a persistent feeling of needing to go even after you’ve finished. Cramping and bleeding centered in the lower abdomen are typical during flares, sometimes accompanied by fatigue and fever.
Crohn’s disease, which can affect any part of the digestive tract, more often causes belly pain with nonbloody diarrhea and unintended weight loss, particularly when the small intestine is involved. Bleeding is possible with Crohn’s but less consistently present than with ulcerative colitis.
When Bleeding Could Signal Cancer
Colorectal cancer accounts for roughly 3.4% of rectal bleeding cases. It’s not the most likely explanation, but it’s the one that matters most to rule out. The bleeding itself doesn’t reliably distinguish cancer from benign causes. Dark versus bright red blood, for example, has no significant predictive value for cancer.
What does raise concern is the combination of symptoms. When rectal bleeding occurs alongside a change in bowel habits, the likelihood of cancer rises to about 9%. Specifically, if your stools have become looser or more frequent along with bleeding, the predictive value climbs to around 12%. Bleeding without any perianal symptoms like itching or a visible lump also carries a higher predictive value (about 11%) compared to bleeding with those symptoms (2%). Age over 60 is another important factor. In one study, 36% of cancer patients had a mass that could be felt during a rectal exam, meaning many cases are detectable with basic evaluation.
Colorectal cancer screening is now recommended starting at age 45 for people at average risk, down from the previous threshold of 50. Options range from annual stool-based tests you can do at home to a colonoscopy every 10 years.
What Happens When You See a Doctor
A medical evaluation for rectal bleeding usually starts with questions about the color, frequency, and amount of blood, along with any changes in bowel habits, pain, or weight loss. A physical exam typically includes a digital rectal exam, where a gloved finger is inserted to feel for masses, tenderness, or hemorrhoids. This takes about a minute and can detect problems in the lower rectum.
If a closer look is needed, the next step is often an anoscopy, a quick in-office procedure using a small, tapered scope to visually inspect the anal canal and check for hemorrhoids, fissures, or other lesions. This can be mildly uncomfortable but is usually tolerable without sedation.
A colonoscopy may be recommended if the cause isn’t obvious from the initial evaluation, if you’re due for cancer screening, if you have a family history of colorectal cancer, or if your symptoms raise concern for something beyond a simple anorectal problem. This involves a full bowel preparation beforehand and sedation during the procedure, with the scope examining the entire colon.
Signs You Need Urgent Care
Most rectal bleeding doesn’t require an emergency room visit, but certain situations do. Large volumes of blood, meaning you’re passing clots or the toilet water turns deep red, need prompt evaluation. Feeling lightheaded, dizzy, or faint alongside bleeding suggests enough blood loss to affect your circulation. A rapid heartbeat, feeling clammy or cold, or confusion are signs your body is struggling to compensate for blood loss and you should get emergency help immediately.
Bleeding that’s accompanied by severe abdominal pain, high fever, or vomiting also warrants urgent evaluation, as these can indicate a serious infection or a condition requiring immediate treatment. Black tarry stools, even without other symptoms, should prompt a call to your doctor the same day since upper GI bleeding can be harder to gauge by volume alone.