Blood in your stool can look bright red, dark red, or black and tarry, depending on where the bleeding originates in your digestive tract. Sometimes it’s obvious on the toilet paper or in the bowl. Other times, it’s completely invisible to the naked eye and only detectable through testing. Knowing what to look for, and what can mimic the appearance of blood, helps you figure out whether what you’re seeing is actually bleeding.
What Blood in Stool Actually Looks Like
Blood changes appearance as it travels through your digestive system. If the bleeding starts low in the digestive tract, near the rectum or anus, you’ll typically see bright red blood. It might streak across the surface of your stool, drip into the toilet bowl, or show up when you wipe. This type of bleeding is the easiest to spot.
If the bleeding starts higher up, in the stomach or upper intestines, the blood gets broken down by digestive enzymes as it moves through. By the time it reaches your stool, the hemoglobin in the blood has turned dark. The result is black, tarry stool that often has a distinctly foul smell. This looks very different from normal dark brown stool. Tarry stool tends to be sticky and almost shiny.
Dark red or maroon-colored stool falls somewhere in between and usually points to bleeding in the middle portion of the digestive tract, like the small intestine or the right side of the colon.
Foods and Medications That Mimic Blood
Before you assume 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 fresh blood. On the darker end, black licorice, blueberries, blood sausage, iron supplements, activated charcoal, and bismuth-based medications like Pepto-Bismol can all turn stool black. These color changes are harmless and typically resolve within a day or two after you stop consuming the culprit.
If you haven’t eaten anything unusual and haven’t started a new supplement, the discoloration is more likely to be actual blood.
Blood You Can’t See
Not all bleeding is visible. Small amounts of blood can mix into stool without changing its color at all. This is called occult (hidden) blood, and it can go unnoticed for weeks or months. Over time, even small amounts of chronic bleeding lead to iron deficiency. You might notice fatigue, weakness, pale skin, shortness of breath during normal activities, or feeling lightheaded. These are signs of anemia from gradual blood loss, and they’re worth investigating even if your stool looks completely normal.
At-Home Stool Tests
If you suspect hidden blood, at-home stool tests can detect it. There are two main types available.
A fecal immunochemical test (FIT) looks for hemoglobin from the lower digestive tract. You collect a small stool sample using a stick or brush included in the kit, place it in a container, and mail it to a lab. No dietary preparation is needed. This test is recommended annually for routine colorectal cancer screening.
A guaiac fecal occult blood test (gFOBT) can detect bleeding from both the upper and lower digestive tract. This one requires some preparation: you may need to avoid red meat, vitamin C, iron supplements, aspirin, ibuprofen, and blood thinners for several days before collecting your sample, since these can interfere with results.
A third option, the stool DNA test, checks for both blood and abnormal DNA markers. It requires a prescription, and the kit includes a container that attaches to your toilet for collection. It’s recommended every three years. All of these tests are simple and accurate, though a positive result will typically lead to a follow-up colonoscopy to identify the source of bleeding.
Common Causes of Bloody Stool
Hemorrhoids are the most common cause. These swollen veins in the rectum or anus often develop from straining during bowel movements due to constipation. They typically produce bright red blood on the toilet paper or in the bowl and are usually not serious.
Anal fissures, which are small tears in the lining of the anal canal, also cause bright red bleeding and tend to be painful during bowel movements. They’re common after passing large or hard stools.
Colon polyps and colorectal cancer can bleed when stool rubs against abnormal tissue as it passes through. This bleeding may be bright red or dark, and it can be intermittent, making it easy to dismiss. Inflammatory bowel disease, which includes Crohn’s disease and ulcerative colitis, is another cause that often comes with additional symptoms like abdominal pain, diarrhea, and weight loss.
Blood-thinning medications, anti-clotting drugs, and medications that irritate the digestive tract (like aspirin and ibuprofen) can also trigger bleeding. If you’re on any of these and notice blood in your stool, that’s important context for your doctor.
What Your Doctor Will Want to Know
The details you notice at home are genuinely useful for narrowing down the source of bleeding. Pay attention to the color of the blood (bright red, dark red, or black), whether it’s on the surface of the stool or mixed in, whether it’s in the toilet water, and whether you notice it only when wiping. Note how often it happens and whether it comes with pain, changes in bowel habits, or abdominal discomfort.
Your doctor will also ask about your current medications, including over-the-counter pain relievers and supplements. Family history of colorectal cancer, inflammatory bowel disease, or other digestive conditions matters too. Having these details ready makes the conversation more productive and helps your doctor decide which tests to order.
Signs That Bleeding Is Urgent
Most causes of blood in stool are not emergencies, but some situations require immediate attention. If you’re passing blood and also feel faint, dizzy, or lightheaded, that suggests significant blood loss and warrants an emergency room visit. Large volumes of bright red blood, blood clots, or rapid onset of symptoms alongside a racing heartbeat, confusion, or cold and clammy skin are also red flags. Black, tarry stool combined with weakness or vomiting that looks like coffee grounds points to active upper digestive bleeding that needs urgent evaluation.