Blood in your stool usually comes from somewhere along your digestive tract, and the cause ranges from something minor like hemorrhoids to something that needs prompt medical attention. In a study of 120 patients with rectal bleeding, hemorrhoids and anal fissures together accounted for about 74% of cases. That said, the color, amount, and accompanying symptoms all matter when figuring out what’s going on.
What the Color Tells You
The color of blood in your stool is one of the most useful clues to where the bleeding is coming from. Bright red blood on the toilet paper or in the bowl typically points to bleeding in the lower part of your digestive tract: the rectum, anus, or lower colon. This is the most common pattern and is often caused by hemorrhoids or small tears near the anus.
Black, tarry stools are a different signal. Blood that starts higher up, in the stomach or upper intestines, gets partially digested as it travels through your system, turning it dark and sticky. This type of bleeding generally needs faster evaluation because the causes tend to be more serious, such as stomach ulcers or inflammation in the upper gut.
Before you panic about color, though, know that certain foods and supplements can fool you. Beets and red food coloring can make stool look reddish. Iron pills, black licorice, blueberries, activated charcoal, and bismuth-based products like Pepto-Bismol can all turn stool black without any bleeding at all.
The Most Common Causes
Hemorrhoids are the single most frequent reason for blood in the stool, responsible for roughly 52% of rectal bleeding cases in one clinical review. These are swollen veins in the lower rectum or anus, similar to varicose veins. Internal hemorrhoids are typically painless but bleed easily, often leaving bright red streaks on toilet paper or dripping into the bowl. External hemorrhoids are more likely to cause pain and discomfort.
Anal fissures are the second most common cause, making up about 21% of cases. A fissure is a small tear in the thin tissue lining the anus, usually from passing a hard or large stool. The bleeding is bright red and often accompanied by a sharp, stinging pain during bowel movements.
Colon polyps, small growths on the lining of the colon, can also bleed. Most polyps are harmless, but some can become cancerous over time if they aren’t removed. Polyps rarely cause noticeable symptoms on their own, so bleeding from a polyp is sometimes the first sign that one exists.
Inflammatory Bowel Disease
Two forms of inflammatory bowel disease, ulcerative colitis and Crohn’s disease, can cause rectal bleeding, but they look quite different. Ulcerative colitis typically causes bloody diarrhea along with urgent trips to the bathroom and a persistent feeling that you haven’t fully emptied your bowels. Because it starts in the rectum and stays in the colon, cramping and bleeding tend to center in the lower abdomen.
Crohn’s disease more often involves belly pain with non-bloody diarrhea and unintended weight loss, especially when the small intestine is affected. Bleeding can still happen with Crohn’s, but it’s less of a defining feature. Both conditions are chronic and involve recurring flare-ups, so if you notice a pattern of digestive symptoms lasting weeks rather than days, that distinction matters.
When Blood in Stool Signals Cancer
Colorectal cancer is the concern most people jump to, and it’s worth understanding the actual picture. Rectal bleeding is a real symptom of colorectal cancer. Almost half of younger adults diagnosed with colon cancer have rectal bleeding as one of their symptoms. But bleeding alone doesn’t mean cancer, and cancer rarely presents with bleeding alone.
The warning signs that raise concern include rectal bleeding combined with a persistent change in bowel habits (new constipation or diarrhea that doesn’t resolve), unexplained weight loss, feeling unusually tired or weak (which can signal slow blood loss causing low iron), bloating, feeling full quickly after eating, or ongoing abdominal pain. A combination of these symptoms, especially lasting more than a few weeks, warrants a thorough evaluation.
The U.S. Preventive Services Task Force recommends that all adults begin routine colorectal cancer screening at age 45 and continue through age 75. If you’re in that window and haven’t been screened, blood in your stool is a good reason to get started.
How Doctors Figure Out the Cause
If you report blood in your stool, your doctor will likely start with a physical exam and questions about color, frequency, and other symptoms. For many people, the next step is a stool test. The fecal immunochemical test (FIT) checks for hidden blood you can’t see with the naked eye. It’s more accurate than older stool tests, with one version detecting advanced growths about twice as often as the older guaiac-based test, while still correctly ruling out problems in over 96% of people without disease.
If a stool test is positive or your symptoms suggest something beyond hemorrhoids, your doctor may recommend a closer look. A sigmoidoscopy uses a flexible camera to examine the rectum and the lowest portion of the colon. It’s often the first step when symptoms point to that specific area, such as lower rectal bleeding, lower abdominal pain, or a sudden change in bowel habits.
If a sigmoidoscopy finds polyps, signs of cancer, or anything abnormal, a full colonoscopy follows. A colonoscopy examines the entire colon and allows the doctor to remove polyps during the same procedure. If you haven’t had a colonoscopy in the past one to two years and something abnormal is found, you’ll need one to get the complete picture.
Signs That Need Immediate Attention
Most rectal bleeding is not an emergency, but certain combinations of symptoms call for urgent care. If rectal bleeding is continuous, heavy, or paired with severe abdominal pain or cramping, go to an emergency room.
Call 911 if you have significant rectal bleeding along with any signs of shock:
- Rapid, shallow breathing
- Dizziness or lightheadedness when standing
- Blurred vision or fainting
- Confusion or nausea
- Cold, clammy, pale skin
- Very low urine output
These signs mean your body is losing blood faster than it can compensate. This is rare, but it’s the one situation where waiting is genuinely dangerous. For non-emergency bleeding that persists for more than a couple of days, or that keeps recurring, scheduling an appointment with your doctor is the right next step. Even when the cause turns out to be something benign like hemorrhoids, getting a clear answer removes the uncertainty.