Blood in your stool usually comes from somewhere along your digestive tract, and the cause ranges from something minor like hemorrhoids to something that needs prompt medical attention like an ulcer or, less commonly, colorectal cancer. The color of the blood is one of the most useful clues to where it’s coming from and how seriously to take it.
What the Color Tells You
Bright red blood typically originates lower in the digestive tract, near the rectum or anus. You might see it on toilet paper, on the surface of your stool, or in the bowl. This is the most common presentation and, while it can be alarming, often points to a cause that’s easily treatable.
Black, tarry stool signals bleeding higher up, usually from the stomach or upper small intestine. Blood turns dark as it travels through the gut because digestive enzymes break down hemoglobin, the protein that gives blood its red color. By the time it reaches the other end, it looks black and has a distinctive sticky, tar-like consistency. This type of bleeding generally warrants faster evaluation because the causes tend to be more serious, such as stomach ulcers or irritation of the esophagus.
Maroon-colored stool falls in between. It can indicate bleeding from the middle of the digestive tract, like the small intestine or the right side of the colon.
Common Causes That Aren’t Dangerous
Hemorrhoids are the single most frequent reason people notice blood after a bowel movement. These swollen blood vessels around the anus bleed easily, especially during straining. The blood is bright red and usually painless, though external hemorrhoids can itch or ache.
Anal fissures are small tears in the lining of the anus, extremely common in infants, pregnant women, and adults under 40. They produce fresh red blood along with a sharp, tearing pain during bowel movements that can linger for minutes to hours afterward. Some people describe the pain as burning or cutting, and it can radiate to the buttocks, thighs, or lower back. Most fissures heal on their own within a few weeks with softer stools and basic care.
Hard stools from constipation can also scrape the rectal lining enough to produce a small streak of blood. This is usually a one-time or occasional event that resolves when your bowel habits normalize.
More Serious Possible Causes
Diverticular bleeding is the most common cause of significant lower GI bleeding. Diverticula are small pouches that form in the colon wall, and they become increasingly common with age: over 50% of people above 60 have them, and that number climbs past 60% after age 80. Most people with diverticula never have symptoms, but when a blood vessel near one of these pouches ruptures, the bleeding can be sudden and heavy. It often stops on its own, but large-volume bleeding needs medical evaluation.
Inflammatory bowel diseases like Crohn’s disease and ulcerative colitis cause chronic inflammation in the digestive tract. Bloody diarrhea, cramping, and urgency are hallmark symptoms. These conditions tend to flare and remit over time and require ongoing management.
Stomach and duodenal ulcers, often caused by a bacterial infection or long-term use of pain relievers, can bleed slowly or rapidly. Slow bleeding may only show up as black, tarry stools or unexplained fatigue from gradual blood loss. Rapid bleeding is a medical emergency.
When Bleeding Could Signal Cancer
Rectal bleeding is considered a red-flag symptom for colorectal cancer, but the actual risk is lower than most people fear. In a large population study, men who visited their doctor with rectal bleeding had roughly a 1.7% chance of being diagnosed with advanced colon cancer. For women with rectal bleeding, the figure was similar, around 1.3%. So while cancer is on the list of possibilities, it accounts for a small minority of cases.
The features that raise more concern include bleeding that persists for weeks, a change in bowel habits (new constipation, narrower stools, or ongoing diarrhea), unintentional weight loss, and fatigue that doesn’t have another explanation. A combination of rectal bleeding and a change in bowel habits is more worrisome than either symptom alone. Routine colorectal cancer screening is recommended for all adults starting at age 45 and continuing through age 75.
Medications and Foods That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets, tomato sauce, cranberries, red peppers, red gelatin, and red drinks can all turn stool red enough to look like blood. On the dark end, iron supplements, bismuth-based stomach remedies like Pepto-Bismol, black licorice, Oreos, and grape juice can make stool appear black without any actual bleeding.
These false alarms are the most common cause of red stools in children. If your stool returns to its normal color within a day or two after stopping the suspect food or supplement, bleeding probably wasn’t the issue.
Medications That Increase Real Bleeding Risk
Common over-the-counter pain relievers significantly raise the risk of upper GI bleeding. Standard anti-inflammatory drugs like ibuprofen and naproxen roughly quadruple the risk compared to not taking them. Low-dose aspirin triples it. Even newer, supposedly gentler anti-inflammatory options still nearly triple the risk. Combining any of these with each other, or with blood thinners or corticosteroids, pushes the risk higher still.
If you take any of these regularly and notice dark or tarry stools, that medication history is important information for your doctor.
Signs You Need Immediate Care
Most rectal bleeding doesn’t require an emergency room visit. A small amount of bright red blood with an obvious explanation, like straining during constipation or a known hemorrhoid, can typically wait for a scheduled appointment.
Seek immediate care if bleeding is heavy or won’t stop, or if it comes with dizziness or faintness, a racing pulse, difficulty urinating, cold or clammy skin, or confusion. These are signs of significant blood loss. Black, tarry stools accompanied by weakness or lightheadedness also warrant urgent evaluation, since slow upper GI bleeding can cause substantial blood loss before you realize how much you’ve lost.
What to Expect at the Doctor
Your doctor will want to know the color of the blood, how much there was, how long it’s been happening, whether it’s on the surface of the stool or mixed in, and whether you have pain. They’ll also ask about your bowel habits, diet, medications, and family history of GI disease or colorectal cancer.
A stool test can detect hidden blood you can’t see with the naked eye. The newer version of this test, called FIT, is more accurate than the older type. It correctly identifies people without bleeding about 92% of the time, compared to 76% for the older test, which means fewer false positives and unnecessary follow-up procedures.
If the cause isn’t obvious, a colonoscopy or upper endoscopy lets the doctor look directly at the lining of your digestive tract and, if needed, treat a bleeding source during the same procedure. For most people, the preparation (clearing out the bowel beforehand) is the most unpleasant part. The procedure itself is done under sedation.