Blood in your poop is most often caused by hemorrhoids or small tears in the skin around the anus. These two conditions account for the majority of cases, especially in adults under 50. But blood in the stool can also signal infections, inflammatory bowel disease, or, less commonly, colorectal cancer. The color of the blood and the symptoms that come with it are strong clues to what’s going on.
What the Color of the Blood Tells You
Bright red blood, the kind you see on toilet paper or sitting on top of the stool, almost always comes from the lower part of the digestive tract: the rectum or the anus. The blood is fresh because it hasn’t traveled far. This is the most common type people notice, and it’s usually tied to hemorrhoids, fissures, or other conditions close to the exit.
Dark red or maroon-colored blood mixed into the stool typically comes from higher up in the colon. Possible causes include diverticular bleeding, inflammatory bowel disease, or polyps. Black, tarry stool with a distinct smell usually means the bleeding started in the upper digestive tract, such as the stomach or the first part of the small intestine. The blood turns dark because stomach acid breaks it down during digestion. Upper GI bleeding from ulcers or inflamed stomach lining can produce this appearance, though bleeding from the right side of the colon occasionally looks the same way.
Hemorrhoids
Hemorrhoids are swollen veins in the lower rectum and anus, similar to varicose veins in the legs. They’re extremely common. Internal hemorrhoids, which form inside the rectum, are often painless and typically show up as bright red blood on the toilet paper or dripping into the bowl. You might not even know they’re there until you see the blood. External hemorrhoids, which develop under the skin around the anus, tend to cause a dull ache, pressure, or irritation. They can become suddenly and intensely painful if a blood clot forms inside them.
Straining during bowel movements, sitting on the toilet for long periods, chronic constipation, and pregnancy all increase the risk. Most hemorrhoids resolve on their own or with simple measures like more fiber, more water, and over-the-counter creams.
Anal Fissures
An anal fissure is a small tear in the thin tissue lining the anus. It causes bright red blood on the toilet paper, similar to hemorrhoids, but the pain is very different. People with fissures describe a sharp, searing sensation during a bowel movement, sometimes compared to passing shards of glass. That sharp pain is often followed by a deep ache lasting minutes to hours afterward.
Fissures are commonly caused by passing hard or large stools. They can also develop during episodes of diarrhea. Most heal within a few weeks with stool softeners and warm baths, though chronic fissures sometimes need further treatment.
Infections
Certain bacterial infections cause bloody diarrhea, sometimes with cramping, fever, and nausea. The most common culprits in the developed world are Campylobacter, certain strains of E. coli (including O157:H7), Salmonella, Shigella, and Yersinia. These typically come from contaminated food or water.
The pattern of symptoms can hint at which pathogen is involved. A high fever (above about 102°F) raises suspicion for Shigella, while E. coli O157:H7 infections often cause bloody diarrhea without much fever at all. Most of these infections run their course in a week or so, but some, particularly E. coli O157:H7, can cause serious complications, especially in young children and older adults. A stool sample can identify the specific bacteria.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease are chronic conditions where the immune system attacks the lining of the digestive tract, causing inflammation and ulcers. Ulcerative colitis specifically targets the colon and rectum, and bloody diarrhea is one of its hallmark symptoms. People with active ulcerative colitis often experience abdominal cramping, urgency to have a bowel movement (sometimes without being able to go), fatigue, weight loss, and fever.
The exact cause involves a combination of genetics, immune system malfunction, imbalances in gut bacteria, and environmental triggers. It tends to run in families and usually develops in early adulthood, though it can appear at any age. Crohn’s disease can affect any part of the digestive tract and may cause bleeding as well, though less consistently than ulcerative colitis. Both conditions are managed long-term with medications that reduce inflammation and calm the immune response.
Diverticular Bleeding
Diverticula are small pouches that form in the wall of the colon, most commonly in people over 40. They’re usually harmless and cause no symptoms. But occasionally a blood vessel next to one of these pouches breaks open, causing sudden, painless bleeding that can be surprisingly heavy. You might see a large amount of dark red or maroon blood in the toilet. Diverticular bleeding stops on its own in most cases, but heavy or persistent episodes sometimes require a hospital visit.
Colorectal Polyps and Cancer
Polyps are growths on the inner lining of the colon. Most are benign, but some can slowly develop into cancer over years. Both polyps and colorectal cancer can bleed, often in small amounts that aren’t visible to the naked eye. When they do produce visible blood, it’s usually mixed into the stool rather than sitting on the surface.
This is why routine screening matters even when you feel fine. The CDC recommends that most people begin colorectal cancer screening at age 45, with regular screening continuing through age 75. A simple at-home stool test called the fecal immunochemical test (FIT) can detect hidden blood with about 96% sensitivity for colorectal cancer. It’s done once a year. Colonoscopy, the most thorough option, is recommended every 10 years for people at average risk. Other options include a FIT-DNA test every three years or a virtual colonoscopy every five years.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stool appear reddish, closely mimicking blood. On the darker side, iron supplements, black licorice, blueberries, blood sausage, activated charcoal, and bismuth-containing medications like Pepto-Bismol can all turn stool black. These changes are harmless, but if you’re unsure whether you’re seeing food coloring or actual blood, stopping the suspected food for a day or two will usually give you your answer.
When Rectal Bleeding Is an Emergency
Most causes of blood in the stool aren’t emergencies, but some situations require immediate attention. Call 911 if you have significant rectal bleeding along with any signs of shock: rapid or shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These signs mean your body is losing blood faster than it can compensate.
Get to an emergency room if the bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping. Steady, heavy bleeding that fills the toilet bowl or doesn’t slow down is not something to monitor at home.
For smaller amounts of blood that appear once or twice and then stop, particularly bright red blood on the toilet paper, it’s reasonable to bring it up at your next doctor’s visit rather than rushing to the ER. But recurring blood in the stool, even in small amounts, warrants investigation, especially if you’re over 45, have a family history of colorectal cancer, or notice changes in your bowel habits alongside the bleeding.