Blood in your poop usually comes from somewhere along the digestive tract, and the cause ranges from something as common as hemorrhoids to something that needs prompt medical attention like an ulcer or inflammatory bowel disease. Most of the time, the culprit is minor, but the color, amount, and accompanying symptoms all matter in narrowing down what’s going on.
What the Color of the Blood Tells You
The appearance of blood in your stool is one of the most useful clues about where the bleeding originates. Bright red blood on the toilet paper or coating the surface of your stool typically points to a source near the end of the digestive tract: the rectum, anus, or lower colon. This is the most common presentation, and it often turns out to be hemorrhoids or a small tear in the anal lining.
Dark, tarry, sticky stool with a distinctly foul smell (called melena) signals bleeding higher up, usually in the stomach or upper small intestine. Blood that travels through the full length of the digestive tract gets broken down along the way, turning it black rather than red. It takes roughly 100 to 200 cc of blood in the upper GI tract to produce this tarry appearance. Maroon or dark red blood mixed throughout the stool often indicates bleeding somewhere in between, like the small intestine or the right side of the colon.
Hemorrhoids and Anal Fissures
These are the two most common causes of visible rectal bleeding, and they share similar triggers. Both tend to develop from straining during bowel movements, chronic constipation, or passing hard stools. Hemorrhoids are swollen blood vessels in or around the rectum that can bleed when irritated. They don’t always hurt, which is why some people notice blood before they notice anything else.
Anal fissures are small tears in the thin, delicate lining of the anus. That lining is more fragile than regular skin, so stretching and straining can rip it. If the muscles surrounding the anus (the sphincters) are overly tight, they add extra tension to this lining, making tears more likely and even reducing blood flow to the tissue, which slows healing. About 90% of fissures cause pain, particularly a sharp or burning sensation during a bowel movement, which distinguishes them from hemorrhoids. Fissures are especially common in infants and during pregnancy, and about half of all cases occur before age 40.
Colon Polyps
Polyps are small growths on the inner wall of the colon. Most cause no symptoms at all, which is why routine screening matters. When polyps do bleed, you might notice blood on your underwear, on toilet paper, or mixed into your stool. The blood can appear as red streaks or can make stool look darker. Over time, slow bleeding from polyps can lead to iron deficiency anemia, causing fatigue and weakness before you ever spot visible blood.
Some polyps are completely benign, while others are precancerous. The U.S. Preventive Services Task Force recommends colorectal cancer screening for all adults starting at age 45, continuing through age 75. The two most common options are a stool-based test (FIT) done every year or a colonoscopy every 10 years. If you’re noticing blood and you haven’t been screened, that’s a good reason to get started.
Inflammatory Bowel Disease
Crohn’s disease and ulcerative colitis both involve chronic inflammation in the digestive tract, and bloody stool is a hallmark symptom of both. Ulcerative colitis specifically targets the colon and rectum, so bloody diarrhea is often one of the earliest signs. Crohn’s can affect any part of the GI tract and may cause bleeding along with abdominal pain, diarrhea, weight loss, and fatigue. These conditions tend to flare and remit over time, so bleeding may come and go.
Diverticular Bleeding
Diverticulosis occurs when small pouches form and push outward through weak spots in the colon wall. This is extremely common with age, and most people never know they have it. Occasionally, a blood vessel near one of these pouches erodes and bleeds. Diverticular bleeding tends to be sudden and painless, sometimes producing a large amount of maroon or bright red blood. It often stops on its own, but heavy episodes need medical evaluation.
Infections That Cause Bloody Diarrhea
Several types of bacterial infection can inflame the intestinal lining enough to cause visible bleeding. Certain strains of E. coli, particularly E. coli O157:H7 (the most common strain causing bloody diarrhea in North America), produce toxins that damage the colon wall. Campylobacter, Salmonella, and Shigella can also cause bloody diarrhea, typically alongside cramping, fever, and nausea. These infections usually come from contaminated food or water and resolve within a week or so, though some, like toxin-producing E. coli, can lead to serious complications including kidney damage.
Ulcers and Stomach Bleeding
Peptic ulcers, open sores in the lining of the stomach or the upper part of the small intestine, can bleed slowly or heavily. The most common causes are infection with H. pylori bacteria and regular use of NSAIDs like ibuprofen, naproxen, or aspirin. A large study in The Lancet found that current NSAID use nearly quintupled the risk of upper GI bleeding compared to non-use, with high doses carrying about seven times the risk and low doses about two and a half times the risk. Ibuprofen carried the lowest relative risk among common NSAIDs, while some others posed risks more than 10 times baseline. The danger increases further if you’re older, smoke, have a history of ulcers, or take blood thinners or corticosteroids at the same time.
Because ulcer bleeding happens high in the digestive tract, it typically shows up as black, tarry stool rather than red blood. If you’re taking NSAIDs regularly and notice this kind of stool change, that’s worth flagging to your doctor promptly.
Foods and Supplements That Mimic Blood
Not everything that looks like blood in your stool actually is. Beets, tomato soup, red gelatin, and foods with red dye can all turn stool reddish. Red meat, including processed meats and liver, can cause a positive result on some stool tests even without actual bleeding. Iron supplements commonly turn stool very dark or black, which can look alarmingly similar to the tarry appearance of upper GI bleeding but lacks the sticky, foul-smelling quality. If you’ve recently eaten something red or started an iron supplement, that’s worth considering before panicking.
If you’re preparing for a fecal occult blood test (the kind that detects hidden blood), you’ll typically be asked to avoid red meat, raw fruits and vegetables (especially melons, radishes, and horseradish), vitamin C above 250 mg per day, and NSAIDs for several days before collecting samples, since all of these can skew results.
Signs That Need Immediate Attention
A small amount of bright red blood on toilet paper after a hard bowel movement is common and usually not an emergency. But certain combinations of symptoms signal that you need care right away. Call 911 if rectal bleeding comes with signs of significant blood loss: rapid, shallow breathing, dizziness or lightheadedness when standing, blurred vision, fainting, confusion, cold or clammy skin, or very low urine output. These suggest your body is losing more blood than it can compensate for.
You should also get to an emergency room if the bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping. Heavy bleeding from the GI tract can escalate quickly, and earlier intervention makes a significant difference in outcomes.