Hemorrhoids are the most common cause of blood in stool, but the list of possibilities ranges from minor tears in the skin around the anus to serious conditions like colorectal cancer. The color and amount of blood, along with any other symptoms you’re experiencing, can help narrow down what’s going on.
What the Color of Blood Tells You
The color of blood in your stool is a useful clue because it signals where in your digestive tract the bleeding is coming from. Bright red blood generally starts lower in the digestive tract, in the colon, rectum, or anus. Dark red or maroon blood often comes from somewhere in the middle, like the small intestine or upper colon. Black, tarry stools point to bleeding much higher up, typically in the stomach or upper small intestine, where the blood has been partially digested during its journey through your system.
Hemorrhoids and Anal Fissures
Hemorrhoids are swollen veins in your rectum or anus, and they’re by far the most frequent reason people notice blood after a bowel movement. They typically develop from straining due to constipation, sitting for long periods, or during pregnancy. You might see bright red blood on the toilet paper, on the surface of your stool, or dripping into the bowl. Most hemorrhoids don’t actually cause pain, though external ones can be uncomfortable. You may also notice itching or small lumps around the anus.
Anal fissures are small tears in the lining of the anal canal, also commonly caused by straining or passing hard stools. They produce similar bright red bleeding, but the key difference is pain. Fissures tend to cause a sharp or burning pain during and after bowel movements, sometimes lasting minutes to hours. If you’re experiencing significant pain along with the bleeding, a fissure is more likely than a hemorrhoid. Both conditions can usually be diagnosed with a simple physical exam.
Diverticular Bleeding
Diverticular bleeding is the most common cause of sudden, significant lower digestive tract bleeding in adults. It happens when small pouches that form in the colon wall (diverticula) develop fragile blood vessels that rupture. Unlike the small amounts of blood you’d see with hemorrhoids, diverticular bleeding tends to produce a large volume of bright red or maroon blood, often enough to require hospitalization. The bleeding is usually painless, which distinguishes it from diverticulitis, where those same pouches become infected and inflamed and cause abdominal pain.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both fall under the umbrella of inflammatory bowel disease, but they affect the digestive tract differently and produce different patterns of bleeding. Ulcerative colitis targets the large intestine and typically causes bloody diarrhea, urgent trips to the bathroom, and a persistent feeling that you still need to go even after a bowel movement. Crohn’s disease more often involves the small intestine and tends to cause belly pain with nonbloody diarrhea and unintended weight loss, though it can cause bleeding when the colon is involved.
Both conditions are chronic and tend to flare and remit over time. If you’re noticing blood in your stool along with ongoing diarrhea, cramping, or unexplained weight loss, these are conditions worth investigating.
Infections That Cause Bloody Stool
Certain bacterial infections can inflame the lining of the intestines and cause bloody diarrhea. E. coli and C. difficile are among the more common culprits. Gastroenteritis, a general term for stomach and intestinal infections (often from contaminated food or water), can also produce blood-streaked diarrhea. These infections usually come on suddenly and are accompanied by cramps, nausea, and sometimes fever. Most resolve on their own, though some bacterial infections need treatment.
Stomach and Upper GI Causes
Peptic ulcers are open sores in the stomach or upper small intestine caused by stomach acid eroding the protective lining. When these ulcers bleed, the blood travels through the entire digestive tract and gets broken down along the way. The result is stool that looks dark, black, and tarry rather than red. This type of bleeding can be easy to miss because it doesn’t look like blood at first glance.
Pain relievers like aspirin, ibuprofen, and naproxen (NSAIDs) are a significant contributor to this kind of upper digestive tract damage. These medications can injure the stomach and duodenal lining with regular use. Risk factors for NSAID-related bleeding include being over 64, having a history of GI problems, or taking low-dose aspirin alongside another NSAID.
Polyps and Colorectal Cancer
Colon polyps are small growths on the inner lining of the colon. Most are harmless, but some can develop into colorectal cancer over time. Both polyps and cancer can bleed when stool passes over them and irritates or damages the abnormal tissue. This bleeding is often slow and not visible to the naked eye, meaning it can go undetected for months or years.
This is one of the main reasons screening matters. The U.S. Preventive Services Task Force recommends that adults begin screening for colorectal cancer at age 45 and continue through age 75. One common screening tool, the fecal immunochemical test (FIT), checks for hidden blood in stool and has a sensitivity of about 96% for detecting colorectal cancer, correctly identifying 24 out of 25 confirmed cases in one large study. A positive FIT is followed by a colonoscopy for a closer look.
Foods and Supplements That Mimic Blood
Not every red stool means bleeding. Beets are the classic example: they can turn both your stool and urine a startling shade of red. Red food dyes, tomato-based sauces, and certain fruits can do the same. Iron supplements often turn stool very dark or black, which can look like the tarry stool associated with upper GI bleeding. If you’ve recently eaten any of these foods, it’s worth waiting a day or two to see if the color returns to normal before worrying.
Blood thinners and anticlotting medications can also cause or worsen bleeding in the digestive tract, so if you’re on these medications and notice blood in your stool, that connection is worth discussing with your doctor.
Signs That Need Immediate Attention
A small amount of bright red blood on toilet paper after a hard bowel movement is common and often harmless. But certain combinations of symptoms signal that something more serious may be happening. Heavy or continuous rectal bleeding, especially alongside severe abdominal pain or cramping, warrants a trip to the emergency room.
If you’re experiencing rectal bleeding along with any signs of significant blood loss, call 911. Those signs include rapid or shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, and reduced urine output. These symptoms suggest your body isn’t circulating enough blood, and that requires urgent care.