Bloody stool is any visible or hidden blood in your bowel movements. It can show up as bright red streaks on toilet paper, red or maroon-colored stool, or black, tarry stool that looks like coffee grounds. The color tells you a lot about where the bleeding is coming from: bright red generally points to the lower digestive tract (colon, rectum, or anus), while black and tarry stool usually signals bleeding higher up, in the stomach or esophagus.
What the Color of Blood Tells You
Bright red blood passed with or on the surface of stool is called hematochezia. It typically originates in the colon or rectum, though very rapid bleeding from the stomach can occasionally produce red blood too. You might notice it in the toilet bowl, mixed into the stool, or on the tissue after wiping.
Black, tarry stool is called melena. Blood turns dark as it travels through the digestive tract and gets broken down by stomach acid and enzymes. By the time it reaches the toilet, it looks black and sticky and often has a distinctly foul smell. Melena most commonly comes from the esophagus, stomach, or upper small intestine. Occasionally, slow bleeding from the right side of the colon can also produce dark stool.
There’s also a third category: occult blood. This is blood present in such small amounts that you can’t see it at all. It’s only detectable through lab tests, which is one reason routine screening matters even when everything looks normal.
Common Causes of Bright Red Blood
Hemorrhoids are the single most common cause of rectal bleeding. These are swollen veins inside the rectum or around the anus, and they’re extremely common. Straining during bowel movements, pregnancy, and heavy lifting all increase pressure on these veins. Hemorrhoid bleeding is typically painless and shows up as bright red drops on tissue or in the bowl.
Anal fissures, small tears in the lining of the anal canal, are another frequent culprit. They usually happen after passing a hard stool and tend to be more painful than hemorrhoids. Both conditions are linked to constipation, and both can heal on their own, though fissures sometimes need treatment.
Inflammatory bowel disease, which includes ulcerative colitis and Crohn’s disease, causes chronic inflammation in the digestive tract. Bloody diarrhea, often with mucus, is a hallmark of ulcerative colitis in particular. The bleeding tends to be persistent or recurring rather than a one-time event, and it usually comes with other symptoms like cramping, urgency, and fatigue.
Colorectal cancer can also cause rectal bleeding. In younger adults diagnosed with colorectal cancer, rectal bleeding and changes in bowel habits are the two most common symptoms, each occurring in roughly 53% of cases. Left-sided tumors are far more likely to produce visible bleeding (about 62% of cases) compared to right-sided tumors (about 26%). One important detail: nearly 10% of patients in one large study initially assumed their bleeding was from hemorrhoids. Bleeding that persists, changes in frequency, or is accompanied by unexplained weight loss or a new change in bowel habits deserves evaluation regardless of your age.
Common Causes of Dark or Black Stool
Peptic ulcers are the most common cause of acute upper gastrointestinal bleeding. These are open sores in the stomach lining or the first part of the small intestine, often caused by a bacterial infection or long-term use of anti-inflammatory painkillers. Gastritis, or generalized inflammation of the stomach lining, can also produce enough bleeding to turn stool dark.
Esophageal varices are enlarged veins in the esophagus or stomach, most commonly caused by liver cirrhosis. When these veins rupture, the bleeding can be severe and life-threatening. This is less common than ulcers but far more dangerous when it happens.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Beets contain a red pigment called betanin that can turn stool a convincing blood-red color. Red food dyes, tomato-based sauces, and certain candies can do the same. If you ate beets or a heavily dyed food in the last day or two, that’s a likely explanation.
On the dark side, iron supplements commonly turn stool dark green or black. Bismuth-based stomach medications (the pink liquid many people take for upset stomachs) can produce jet-black stool. Even large amounts of black licorice or darkly colored candy can darken things. The key difference is that these color changes don’t come with other symptoms like pain, dizziness, or a tarry, sticky texture.
How Bloody Stool Is Diagnosed
If blood isn’t visible but your doctor suspects hidden bleeding, a stool test can confirm it. The fecal immunochemical test (FIT) uses an antibody that attaches to blood proteins in your stool and is considered more accurate than the older guaiac-based test. FIT requires a sample from one to three separate bowel movements depending on the brand.
When blood is confirmed, the most common next step is a colonoscopy. This involves a thin, flexible tube with a camera that lets a doctor examine the entire colon. If bleeding appears to be coming from higher up, an upper endoscopy examines the esophagus and stomach instead. These procedures can both diagnose and sometimes treat the source of bleeding in the same session, for instance by cauterizing a bleeding ulcer or removing a polyp.
The U.S. Preventive Services Task Force recommends that all average-risk adults begin colorectal cancer screening at age 45. If you have symptoms like bloody stool, screening applies regardless of age.
Signs That Need Immediate Attention
Most rectal bleeding turns out to be something minor, but certain combinations of symptoms signal a medical emergency. Heavy or continuous bleeding that doesn’t stop is one. Severe abdominal pain or cramping alongside bleeding is another.
Signs of significant blood loss require emergency help. These include rapid or shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, and very low urine output. These symptoms suggest your body is losing blood faster than it can compensate, and they warrant calling emergency services rather than driving yourself to a hospital.
A single episode of a small amount of bright red blood, especially if you’ve been constipated or straining, is less alarming. But any rectal bleeding that recurs, persists for more than a couple of days, or is accompanied by weight loss, fatigue, or a change in your usual bowel pattern is worth getting checked out promptly.