Blood in your stool can come from anywhere along your digestive tract, from your esophagus to your rectum. The most common causes are hemorrhoids and small tears in the anal lining, but the list also includes infections, inflammatory bowel disease, pouches in the colon wall, and, less commonly, cancer. What the blood looks like is often the first clue to where it’s coming from.
What the Color of the Blood Tells You
Bright red blood typically originates lower in the digestive tract, near the rectum or anus. You might see it on the toilet paper, on the surface of the stool, or dripping into the bowl. This kind of bleeding is called hematochezia, and it’s the type most people notice first.
Black, tarry stools point to bleeding higher up, in the stomach or upper small intestine. Blood that travels the full length of the digestive tract gets broken down by digestive enzymes along the way, turning the hemoglobin in your blood much darker. The result is a sticky, tar-like stool with a distinctly foul smell. This is called melena, and it generally signals a more serious source of bleeding. Maroon-colored stool falls somewhere in between, often indicating bleeding in the middle portion of the digestive tract or a brisk bleed from the right side of the colon.
Hemorrhoids and Anal Fissures
These two conditions are the most frequent culprits behind bright red blood after a bowel movement, and they’re often confused with each other. Hemorrhoids are swollen blood vessels in or around the anus. They can cause painless bleeding, itching, and noticeable lumps or swelling. Internal hemorrhoids often bleed without much discomfort at all, which is why people are sometimes caught off guard by the amount of red in the toilet.
Anal fissures are small tears in the lining of the anal canal, usually caused by passing hard or large stools. The key difference is pain: fissures tend to cause a sharp, stinging sensation during and after a bowel movement, along with itching or burning that lingers. You’ll typically see blood when you wipe or on the surface of the stool rather than mixed into it. Both conditions can usually be diagnosed during a physical exam, and most cases resolve with dietary changes, more water, and time.
Diverticular Bleeding
Diverticula are small pouches that form in the wall of the colon, most commonly in people over 40. They’re extremely common and usually cause no symptoms at all. But when a blood vessel inside one of these pouches bursts, the bleeding can be sudden and heavy. The hallmark of diverticular bleeding is painless, bright red or maroon-colored blood, sometimes in large volumes. Some people feel cramping or an urgent need to go to the bathroom, but that’s mostly a reaction to blood moving through the colon rather than the bleeding itself. Bleeding from pouches on the left side of the colon tends to be bright red, while bleeding from the right side often appears darker or maroon.
Most diverticular bleeds stop on their own, but the volume of blood loss can be significant enough to cause dizziness or weakness, which warrants immediate medical attention.
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. Ulcerative colitis is especially associated with rectal bleeding. In its mildest form, called ulcerative proctitis, bleeding or urgency may be the only sign of the disease. As inflammation spreads further along the colon, symptoms expand to include bloody diarrhea, abdominal cramps, fatigue, weight loss, fever, and a frustrating sensation of needing to go but being unable to. About half of people with ulcerative colitis experience mild to moderate symptoms.
Crohn’s disease can affect any part of the digestive tract and is more variable in its presentation. Bloody stool is possible but less consistently the defining symptom compared to ulcerative colitis. Both conditions tend to flare and remit over time, and both significantly increase the risk of colorectal cancer over the long term, making regular screening important.
Infections That Cause Bloody Diarrhea
Several bacterial infections can inflame the lining of the colon enough to cause visible blood in your stool. Bacteria like Salmonella, Shigella, Campylobacter, and certain strains of E. coli are common causes. You’ll typically have diarrhea, cramping, and sometimes fever alongside the bleeding. Most of these infections are linked to contaminated food or water and resolve within a week or so, though some require treatment. If you develop bloody diarrhea after traveling, eating undercooked meat, or during a known outbreak, an infection is a likely explanation.
Colorectal Cancer and Polyps
This is the possibility that drives most people to search for answers, and it’s worth addressing directly. Colorectal cancer can cause blood in the stool, but it’s far less common than hemorrhoids or fissures as the actual explanation. Still, it’s the reason screening matters. Polyps, which are small growths on the colon lining, can bleed intermittently and are considered precancerous. Removing them during a colonoscopy is one of the most effective ways to prevent colon cancer from developing in the first place.
The U.S. Preventive Services Task Force recommends that most adults begin routine colorectal cancer screening at age 45 and continue through age 75. That age threshold dropped from 50 to 45 in recent years, partly because early-onset colorectal cancer is rising. Data through 2017 shows that cancer rates in adults between 25 and 49 are increasing in more than half of the 50 countries studied, with some of the sharpest annual increases seen in New Zealand, Chile, Puerto Rico, and England. If you have a family history of colon cancer, a personal history of polyps, or inflammatory bowel disease, screening may need to start earlier and happen more frequently.
Upper GI Bleeding
Bleeding from the stomach or upper intestine, often caused by ulcers or tears in the esophageal lining, usually shows up as black, tarry stool rather than red blood. It can also cause vomiting blood. Accompanying symptoms often include abdominal pain, lightheadedness, dizziness, and in serious cases, fainting. This type of bleeding can lead to rapid blood loss. Tachycardia (a racing heart rate) and a drop in blood pressure are signs that blood loss is significant and needs emergency care.
Foods and Medications That Mimic Blood
Before assuming the worst, it’s worth considering what you’ve eaten or taken recently. Several common substances can change your stool color in ways that look alarming but are completely harmless.
- Beets: A red pigment called betanin can turn stool a convincing blood-red color within a day or two of eating them.
- Iron supplements: These commonly turn stool dark green or black, which can look a lot like the tarry stool caused by upper GI bleeding.
- Bismuth (the active ingredient in Pepto-Bismol): Turns stool jet black.
- Artificial food coloring: Brightly dyed candies, frostings, and drinks can tint your stool unexpected colors. Enough mixed colors can even produce black stool.
If you’ve recently consumed any of these and have no other symptoms, the discoloration is likely harmless. It should clear within a day or two of stopping the food or supplement.
How Blood in Stool Is Evaluated
When blood isn’t visible to the naked eye, stool tests can detect it. A fecal immunochemical test (FIT) or fecal occult blood test (FOBT) checks a stool sample for hidden blood. Both can be done at home with a collection kit, require no preparation like fasting or sedation, and are typically repeated every year as part of routine screening. The trade-off is that these tests can miss some polyps and cancers, and they sometimes flag blood that turns out to be from a benign source.
When stool tests come back positive, or when symptoms are persistent or concerning, a colonoscopy is the next step. It allows direct visualization of the entire colon and the ability to remove polyps or take tissue samples during the same procedure. People with risk factors like a family history of colon cancer, prior polyps, or inflammatory bowel disease are often recommended to go straight to colonoscopy rather than relying on stool-based screening alone.
Signs That Bleeding Needs Urgent Attention
Most rectal bleeding is minor and stops on its own. But certain combinations of symptoms signal that something more serious is happening. Heavy or continuous bleeding, black tarry stools, dizziness or lightheadedness, fainting, a rapid heartbeat, or blood accompanied by severe abdominal pain all point to significant blood loss or a source of bleeding that won’t resolve without intervention. Unexplained weight loss, persistent changes in bowel habits, or bleeding that recurs over weeks also warrant prompt evaluation, even if the amount of blood seems small each time.