Blood in your stool usually comes from somewhere along your digestive tract, and the color tells you a lot about where. Bright red blood typically originates from the lower digestive tract (colon, rectum, or anus), while black, tarry stools point to bleeding higher up, such as the stomach or upper intestines. The most common causes are benign and treatable, but some deserve prompt medical attention.
What the Color of Blood Tells You
Bright red blood on toilet paper, in the bowl, or mixed into your stool means the bleeding source is relatively close to the exit. The blood hasn’t had time to be broken down, so it keeps its red color. This is the type most people notice first, and it’s most often linked to hemorrhoids or small tears near the anus.
Black, tarry stools are a different signal. When blood starts higher in the digestive tract, hemoglobin (the protein that makes blood red) gets broken down by digestive enzymes as it travels through the intestines. By the time it reaches the stool, it’s turned dark and sticky. This type of bleeding can come from stomach ulcers, inflammation in the upper intestines, or other conditions affecting the esophagus or stomach.
Maroon-colored stool falls somewhere in between and can indicate bleeding from the small intestine or the right side of the colon, where blood has been partially digested but not fully broken down.
Hemorrhoids and Anal Fissures
These are the two most common causes of visible blood in stool, and both are tied to straining and constipation. Hemorrhoids are swollen veins inside your rectum or around your anus. They bulge close to the surface, and when the skin over them breaks, they bleed. Pregnancy, heavy lifting, and straining during bowel movements all increase pressure on these veins.
Anal fissures are small tears in the lining of the anal canal. Like hemorrhoids, they often happen after passing a hard stool. The two are easily confused because they share the same triggers and both cause pain and bleeding, though fissures tend to be more painful, especially during a bowel movement. Bright red blood on the toilet paper or coating the outside of the stool is the classic presentation for both.
Diverticular Bleeding
Diverticulosis, the formation of small pouches in the colon wall, becomes increasingly common with age. Most people with these pouches never have symptoms. About 10% experience some bleeding, and roughly 3% need treatment to stop it. When a blood vessel near one of these pouches erodes, it can produce a sudden, painless episode of bright red or maroon blood. Diverticular bleeding often stops on its own but can be heavy enough to require medical evaluation.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease cause chronic inflammation in the digestive tract, and bloody stool is one of their hallmark symptoms. In ulcerative colitis, inflammation targets the inner lining of the colon and rectum, leading to ulcers that bleed. You’ll often see blood mixed with mucus and diarrhea. Crohn’s disease can affect any part of the digestive tract and may cause blood in stool along with abdominal pain, fatigue, and weight loss. Both conditions involve flares that come and go, and the bleeding tends to recur until the underlying inflammation is controlled.
Infections That Cause Bloody Diarrhea
Several types of bacteria can invade the intestinal lining and cause bloody diarrhea, usually accompanied by fever and cramping. The most common culprits include certain strains of E. coli (particularly the type that produces toxins damaging to the gut wall), Salmonella, Shigella, and Campylobacter. A parasitic infection called amoebic colitis can also be responsible, particularly after travel to areas with contaminated water. These infections typically resolve within days to a couple of weeks, though some require antibiotic treatment.
Medications That Increase Bleeding Risk
Common pain relievers like ibuprofen, aspirin, and naproxen can erode the stomach lining over time, especially with regular use. These drugs block a protective enzyme in the stomach wall, leaving it more vulnerable to acid damage and eventually ulceration. Blood thinners compound the problem. A study of elderly patients on the blood thinner warfarin found that adding a standard anti-inflammatory pain reliever nearly doubled their risk of being hospitalized for upper digestive tract bleeding. If you take blood thinners and notice any change in stool color, that’s worth a prompt conversation with your doctor.
Abnormal Blood Vessels in the Colon
In older adults, fragile clusters of widened blood vessels can develop along the colon wall. These are more common after age 60 and can bleed intermittently, sometimes producing bright red blood, sometimes darker stool, and sometimes no visible blood at all, just a slow, steady loss that leads to iron-deficiency anemia over months. The bleeding is often unpredictable, stopping and starting without an obvious trigger.
Colorectal Cancer and Polyps
This is often what people fear most when they search for causes of blood in stool, and it’s an important possibility to address. Colon polyps (growths on the inner wall of the colon) can bleed, and some polyps eventually become cancerous. Colorectal cancer itself can cause persistent blood in the stool, a change in bowel habits, unexplained weight loss, and fatigue from slow blood loss.
Current guidelines from the U.S. Preventive Services Task Force recommend that most people begin screening for colorectal cancer soon after turning 45, continuing through age 75. Screening catches polyps before they become cancerous and detects cancers at earlier, more treatable stages. If you’re noticing blood in your stool and you’re over 45 (or have a family history of colorectal cancer), getting screened is especially important.
Foods and Supplements 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 and look alarmingly like blood. On the dark side, iron supplements, black licorice, blueberries, activated charcoal, and bismuth-based antacids (the active ingredient in Pepto-Bismol) can all turn stool black in a way that resembles tarry, digested blood. The key difference is that these color changes aren’t accompanied by other symptoms like pain, dizziness, or fatigue. If you stop the food or supplement and the color returns to normal within a day or two, that’s usually your answer.
Signs That Need Urgent Attention
Most causes of blood in stool are manageable, but some situations require immediate care. A large volume of blood, especially if it’s maroon or dark and coming frequently, can lead to dangerous drops in blood pressure. Watch for lightheadedness, a racing heartbeat, feeling faint when standing, confusion, or pale skin. These suggest you’re losing blood faster than your body can compensate. Persistent black, tarry stools also warrant urgent evaluation because they indicate ongoing bleeding from the upper digestive tract that you can’t see directly.
A single episode of bright red blood on toilet paper after a hard bowel movement is far less concerning than repeated bleeding, large amounts of blood, or blood accompanied by weight loss, fevers, or changes in your normal bowel pattern. The combination of symptoms, not just the blood itself, helps distinguish routine causes from something that needs investigation.