Blood in diarrhea can look very different depending on where in the digestive tract the bleeding originates. It may appear as bright red streaks or drops, a pinkish or reddish tint mixed throughout the stool, dark maroon clots, or black and tar-like material. Each appearance points to a different cause and a different location of bleeding.
Bright Red Blood
Bright red blood is the most recognizable form. It typically comes from the lower part of the digestive tract: the colon, rectum, or anus. You might see it as streaks on the surface of the stool, drops in the toilet water, or smeared on toilet paper. In some cases, particularly with conditions like diverticulitis or severe colitis, the bleeding can be heavy enough that the toilet bowl looks like it’s filled with blood.
When bright red blood is mixed into diarrhea rather than sitting on top of it, the stool often takes on a pinkish or uniformly red color. This pattern is common with inflammatory bowel conditions like ulcerative colitis, where the lining of the colon is inflamed and bleeding. In those flares, you may also notice mucus or pus mixed in with the bloody stool, along with urgent cramping and a feeling that you need to go even when your bowels are empty.
Dark or Maroon Blood
Blood that appears dark red or maroon usually comes from higher up in the colon or the small intestine. It’s had more time to break down as it moves through the digestive tract, so it loses that fresh, bright red look. Maroon-colored diarrhea often signals more significant bleeding and can be harder to distinguish from certain foods at first glance. If you’re seeing dark red clots or a deep burgundy color in loose stool, that typically points to a source further from the rectum than bright red blood would suggest.
Black, Tarry Stool
When bleeding starts high in the digestive tract, such as the stomach or upper small intestine, the blood is exposed to digestive enzymes as it travels downward. A protein in blood called hemoglobin gets broken down and darkens significantly during that journey. The result is stool that looks black and has a distinctly tarry, sticky texture. It also tends to have an unusually strong, foul smell. This type of stool signals that blood has been digested, and the bleeding source could be quite far from the rectum.
Black tarry stool looks different from stool that’s simply dark brown. The consistency is notably sticky and almost shiny, more like roofing tar than a normal bowel movement.
Blood You Can’t See
Not all blood in diarrhea is visible. Small amounts of bleeding can be completely invisible to the naked eye. This is called occult (hidden) blood, and it’s only detectable through lab testing. A stool test called a FIT (fecal immunochemical test) is the standard screening tool. It’s specific to human blood, requires only a single sample, and doesn’t need any food restrictions beforehand. FIT detects about twice as many cases of cancer and advanced precancerous growths compared to the older guaiac-based tests. If your doctor suspects hidden bleeding, this is likely the test they’ll order.
What Can Mimic Blood in Stool
Before assuming the worst, it’s worth knowing that several foods and medications can make stool look bloody when it isn’t. Beets and foods with red coloring can turn stool reddish, closely mimicking the look of bright red blood. On the dark end, black licorice, blueberries, iron supplements, activated charcoal, and bismuth-containing medications like Pepto-Bismol can all produce black stools that look alarmingly like digested blood. The key difference is texture: medication-related black stool is usually firm and normal in consistency, while true upper GI bleeding produces that distinctive tarry, sticky quality.
Common Causes of Bloody Diarrhea
Bloody diarrhea has a wide range of causes, and the appearance of the blood often narrows down the possibilities.
Bacterial infections are a frequent trigger. Certain strains of E. coli, particularly the Shiga toxin-producing type, cause bloody diarrhea along with severe stomach cramps and vomiting. Other strains can cause watery diarrhea that becomes bloody as the infection progresses. These infections typically come from contaminated food or water and resolve within a week, though some can become serious.
Inflammatory bowel disease, especially ulcerative colitis, is a major cause of recurring bloody diarrhea. The hallmark is diarrhea mixed with blood, mucus, or pus, often accompanied by belly cramps, fatigue, and weight loss. Some people experience bloody diarrhea as their only symptom during mild flares. In more severe or widespread colitis, the bloody diarrhea can be frequent and debilitating.
Hemorrhoids and anal fissures can also produce blood, though they behave differently. Both typically cause bright red blood noticed on toilet paper. Fissures tend to produce small amounts, while hemorrhoids can bleed more noticeably and sometimes produce visible clots. The important distinction is that blood from hemorrhoids and fissures usually isn’t mixed into the stool itself. It coats the outside or appears separately in the toilet bowl.
Signs That Need Immediate Attention
Some combinations of symptoms alongside bloody diarrhea signal a need for emergency care. Large amounts of blood, whether bright red or dark, warrant urgent evaluation. Lightheadedness, a rapid heart rate, or sudden weakness alongside bloody diarrhea can indicate significant blood loss. These symptoms suggest your body is struggling to compensate for the volume of blood being lost, and waiting it out is not safe.
A small amount of bright red blood on toilet paper after a bout of diarrhea, with no other symptoms, is a very different situation from passing large volumes of dark or maroon stool with dizziness. Both deserve medical evaluation, but the second scenario is time-sensitive.