Blood in stool ranges from bright red streaks on toilet paper to black, tar-like bowel movements, and sometimes it’s completely invisible. The color and texture tell you where the bleeding is coming from in your digestive tract, which is why appearance matters so much.
Bright Red Blood
Bright red blood is the most recognizable form. It typically comes from the lower part of the digestive tract: the rectum, anus, or lower colon. You might see it as streaks on the surface of your stool, drops in the toilet water, or smears on the toilet paper. The blood looks fresh because it hasn’t traveled far or been exposed to digestive enzymes.
Hemorrhoids and anal fissures (small tears in the skin around the anus) are the most common sources. With these conditions, the blood is usually on the outside of the stool or only on the tissue, not mixed in. If the blood is more thoroughly mixed into the stool or appears in larger amounts, the source is more likely inside the colon itself, from conditions like pouches in the colon wall, polyps, inflammatory bowel disease, or, less commonly, colorectal cancer.
Maroon or Dark Red Stool
When blood has traveled partway through the digestive system, it darkens from bright red to a maroon or burgundy color. This usually indicates bleeding somewhere in the small intestine or the right side of the colon. The stool may look uniformly dark red or have visible clots mixed in. Maroon stool can also result from very heavy upper digestive bleeding that moves through the intestines quickly, before the blood has time to fully break down.
Black, Tarry Stool
Black, sticky stool with a tar-like consistency is the hallmark of bleeding higher in the digestive tract, typically in the stomach or upper small intestine. Stomach acid converts hemoglobin (the oxygen-carrying protein in red blood cells) into a brown-black compound called hematin, which gives the stool its distinctive dark color and thick texture. This type of stool also tends to have a particularly strong, foul smell.
The key visual difference between this and simply dark stool is the texture. Tarry stool is notably sticky and shiny, almost like roofing tar. It clings to the bowl and is difficult to flush. If your stool is dark but formed normally and doesn’t have that sticky quality, something other than blood may be responsible.
Foods and Medications That Mimic Blood
Several everyday substances can make stool look alarming when there’s no bleeding at all. Beets contain a red pigment called betanin that can turn stool a convincing blood-red. Tomato skins, cranberries, and red gelatin can do something similar. On the dark end, iron supplements often turn stool dark green or black. Bismuth subsalicylate (the active ingredient in Pepto-Bismol) can turn stool jet black. Blueberries and black licorice can also darken things considerably.
The Merck Manual notes that black stool from iron or bismuth does not contain actual blood and shouldn’t be confused with true tarry stool. If you’ve recently eaten beets or started a new supplement, that’s worth considering before worrying. The simplest test: stop the food or supplement for a couple of days and see if the color returns to normal.
Blood You Can’t See
Not all digestive bleeding is visible. Small amounts of blood can be present in normal-looking stool, a situation called occult (hidden) blood. You won’t notice anything unusual in the toilet. This type of bleeding is detected only through lab testing, which is one reason routine screening matters.
The most common screening tool is the fecal immunochemical test, or FIT, which uses antibodies to detect hemoglobin in a stool sample. With a single test, FIT is roughly 80% sensitive for detecting colorectal cancer. For earlier-stage growths like advanced polyps, sensitivity is lower (around 20% to 30% with one test), which is why the test is repeated annually. Occult bleeding can come from polyps, ulcers, inflammatory bowel disease, or cancer, but it can also come from hemorrhoids or other benign sources.
Blood in Infant Stool
In babies, the most common cause of blood in the stool is allergic colitis, a reaction to proteins in cow’s milk. It affects 2 to 3 percent of infants. The blood typically appears as small flecks or thin streaks mixed into the stool, sometimes so faint it’s only visible under a microscope. Affected babies are often fussy and hard to console, and some also have diarrhea, vomiting, or signs of other allergies like eczema.
The treatment is straightforward: if the mother is breastfeeding, she switches to a dairy-free diet. Formula-fed babies are switched to a hypoallergenic formula. About 30 percent of babies with cow’s milk allergy also react to soy protein, so soy may need to be eliminated too if symptoms persist.
A less common but more urgent cause in infants is intussusception, where one section of intestine telescopes into another. This produces a distinctive “currant jelly” stool: dark red, mucus-like, and jelly-textured. This is a medical emergency.
Signs That Bleeding Is Serious
The volume and speed of bleeding matter more than color alone. Small streaks of bright red blood on toilet paper after a hard bowel movement are very common and usually minor. But certain accompanying symptoms signal that bleeding is heavy enough to affect your circulation. According to the National Institute of Diabetes and Digestive and Kidney Diseases, these include:
- Feeling lightheaded, dizzy, or faint
- Shortness of breath
- Rapid heart rate
- Cold or clammy hands and feet
- Pale skin
- Confusion or loss of consciousness
These are symptoms of shock from blood loss and require emergency care. Even without those dramatic signs, any new appearance of black tarry stool warrants prompt medical attention, because upper digestive bleeding can be substantial before you feel its effects. Persistent or recurring blood in the stool, even in small amounts, also deserves evaluation to rule out polyps, inflammatory disease, or cancer.