Blood in stool shows up in three main ways: bright red blood on the toilet paper or in the bowl, dark maroon-colored stool, or black and tarry stool with a distinct foul smell. Each color points to a different location of bleeding in the digestive tract, and some are more urgent than others. Not every color change means bleeding, though. Several common foods and medications can mimic the appearance of blood.
What Blood in Stool Actually Looks Like
The color of the blood tells you a lot about where it’s coming from. Bright red blood, either streaked on the stool surface, dripping into the toilet bowl, or showing up on the toilet paper, generally comes from the lower digestive tract: the colon, rectum, or anus. This is the most common presentation and is often caused by something relatively minor like hemorrhoids or a small tear near the anus.
Dark maroon or burgundy-colored stool suggests bleeding from higher up in the colon or the lower part of the small intestine. The blood has had more time to break down as it travels through the gut, which darkens its color.
Black, sticky, tarry stool with a strong unpleasant odor typically signals bleeding above the colon, often from the stomach or upper small intestine. By the time the blood passes through the entire digestive system, digestive enzymes and stomach acid break it down into a dark, tar-like substance. This type of stool has a distinctive sticky consistency that’s hard to miss.
Sometimes blood is invisible to the naked eye entirely. This is called occult (hidden) blood, and it can only be detected through lab testing. You could have a slow, steady bleed for weeks without any visible change in your stool’s appearance.
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 the look of blood. On the darker end, black licorice, blueberries, blood sausage, iron supplements, activated charcoal, and bismuth-containing medications like Pepto-Bismol can all turn stool black.
A key difference: stool darkened by these substances typically doesn’t have the same tarry, sticky texture or strong odor that true upper GI bleeding produces. If you stop the food or supplement and the color returns to normal within a day or two, bleeding was likely not the cause. If you’re unsure, a simple stool test can give you a definitive answer.
Common Causes of Blood in Stool
Hemorrhoids are the most common cause. These swollen veins in the rectum or anus frequently result from straining during bowel movements due to constipation. The blood is usually bright red, appears on the toilet paper or drips into the bowl, and the bleeding tends to be painless.
Anal fissures, small tears in the lining of the anal canal, are the second most common culprit. They also happen from straining, but unlike hemorrhoids, fissures typically cause sharp pain during and after a bowel movement along with the bleeding.
Inflammatory bowel disease (IBD) causes chronic inflammation in the intestinal lining. Ulcerative colitis primarily affects the colon and rectum, while Crohn’s disease can involve any part of the digestive tract. Both can produce bloody stool, often accompanied by diarrhea, abdominal pain, and weight loss over time.
Diverticular disease occurs when small pouches form in the colon wall. These pouches are common and usually harmless, but if they become inflamed or infected, they can bleed. Diverticular bleeding often comes on suddenly and produces a noticeable amount of maroon or bright red blood, then stops on its own.
Colorectal polyps and colorectal cancer can also cause bleeding, which is one reason screening is so important. These growths often bleed slowly, producing occult blood that you can’t see. Visible blood from a polyp or tumor may be mixed into the stool rather than sitting on the surface.
How to Test for Hidden Blood
If you suspect bleeding but can’t see anything, or if you want confirmation that a color change is actually blood, two types of at-home stool tests exist.
The older method, called a guaiac-based test, detects the chemical component of blood through a reaction on a treated card. It works, but it comes with limitations. You need to avoid red meat, certain raw fruits and vegetables, and vitamin C supplements for three days before testing, because all of these can cause false results. Red meat and some raw produce can trigger false positives, while vitamin C can mask real bleeding and produce false negatives. With a single test, it catches only about 35 to 55 percent of significant bleeding. Repeated annual testing pushes that detection rate up to around 80 percent.
The newer fecal immunochemical test (FIT) specifically targets human blood proteins, which means no dietary restrictions are needed before testing. It won’t react to the steak you had last night or the iron supplement you took this morning. FIT detects 70 to 82 percent of significant cases with a single test while maintaining around 95 percent accuracy in ruling out false alarms. Some versions use a small probe inserted into the stool sample, while others simply require you to sample the toilet bowl water. FIT is now the preferred screening method for most clinical guidelines.
Signs That Bleeding Needs Urgent Attention
Most causes of blood in stool are not emergencies, but certain combinations of symptoms signal significant blood loss that requires immediate medical evaluation. Lightheadedness or dizziness when standing, a racing heartbeat, cold or clammy skin, confusion, and fainting all suggest your body is losing blood faster than it can compensate. Passing large amounts of blood, whether bright red or dark, alongside any of these symptoms warrants a trip to the emergency room.
Black tarry stool deserves prompt attention even without other symptoms, because it indicates active bleeding in the upper digestive tract, which can escalate quickly. The same applies to maroon-colored stool that persists beyond a single bowel movement, especially if you haven’t eaten anything that could explain the color change.
Rectal bleeding that recurs over several weeks, even in small amounts, also warrants investigation. A single episode of bright red blood after straining is commonly a hemorrhoid. But if it keeps happening, if you notice a change in bowel habits alongside it, or if you’re losing weight without trying, those patterns point to something that needs a closer look.