Blood in your stool is common, but it is not normal. Something is causing it, and the range of possibilities spans from a minor hemorrhoid that heals on its own to conditions that need prompt treatment. Most of the time, the cause is not serious, but the blood itself is always worth paying attention to because its color, amount, and accompanying symptoms tell you a lot about where it’s coming from and how urgently you need to act.
What the Color of the Blood Tells You
The color of blood in your stool is a useful clue about its origin. Bright red blood typically comes from the lower part of your digestive tract: the rectum, the anus, or the lower colon. This is the kind you might notice on toilet paper, on the surface of stool, or dripping into the bowl. It’s the most common type people see, and it’s often caused by hemorrhoids or small tears in the skin around the anus.
Black, tarry stool is a different signal. When blood starts higher up in the digestive tract, in the stomach or upper intestine, it gets broken down by digestive enzymes as it travels through your system. By the time it reaches your stool, the blood has turned dark and sticky. This type of bleeding is harder to notice because it doesn’t look like blood at first glance, but it can indicate ulcers, inflammation, or other problems in the upper GI tract and generally warrants quicker medical attention.
Dark red or maroon-colored blood falls somewhere in between and can come from the right side of the colon, where bleeding from small pouches called diverticula is most common.
The Most Common Causes
Hemorrhoids
Hemorrhoids are swollen blood vessels in and around the rectum, and they’re the single most frequent reason people see bright red blood after a bowel movement. Internal hemorrhoids, which form inside the rectum, are painless but tend to bleed. You might see streaks of red on the stool or blood in the bowl. External hemorrhoids sit on the outer tissue around the anus and are more likely to cause itching or discomfort. If a blood clot forms inside an external hemorrhoid, the pain can be severe.
Anal Fissures
An anal fissure is a small tear in the lining of the anus, usually caused by passing hard or large stools. Fissures also produce bright red blood, but the key difference from hemorrhoids is pain. Fissures cause sharp, intense pain during a bowel movement that can linger for minutes or even hours afterward. If you notice blood and significant pain that persists well after you leave the bathroom, a fissure is a likely culprit. Most fissures heal within a few weeks with increased fiber and hydration.
Diverticular Bleeding
Diverticula are small pouches that form in the walls of the colon, especially as people age. They’re extremely common and usually harmless, but occasionally a blood vessel near one of these pouches breaks open. Diverticular bleeding accounts for 30 to 50 percent of cases involving large-volume rectal bleeding, making it the most common cause of sudden, heavy blood in the stool. The bleeding is typically painless, which can be alarming because there’s no warning. You might experience cramping or an urgent need to use the bathroom simply because the blood itself irritates the colon. Most episodes stop on their own, but heavy or prolonged bleeding needs emergency evaluation.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease cause chronic inflammation in the digestive tract that can lead to bloody stool, often mixed with mucus. Unlike a one-time episode from hemorrhoids, IBD-related bleeding tends to recur and comes alongside other symptoms like persistent diarrhea, abdominal pain, fatigue, and unintentional weight loss. If you’re seeing blood in your stool repeatedly over weeks along with changes in your bowel habits, this is a pattern worth investigating.
Medications That Increase Bleeding Risk
Certain medications make GI bleeding more likely, even if you don’t have an obvious injury or disease. Common anti-inflammatory painkillers like ibuprofen and naproxen are among the most well-known culprits. Low-dose aspirin, widely used for heart health, increases the risk of upper GI bleeding by roughly 1.6 to 4 times compared to not taking it.
The risk climbs significantly when these drugs are combined with each other or with other medications. Taking an anti-inflammatory painkiller alongside a corticosteroid, for example, raises the risk of diagnosed upper GI bleeding nearly 13-fold. Combinations with blood thinners increase risk about 9-fold, and even antidepressants in the SSRI class (commonly prescribed for anxiety and depression) can raise bleeding risk 5 to 7 times when paired with painkillers or aspirin. If you take any of these medications regularly and notice blood in your stool, that combination is worth mentioning to your doctor because it may be the explanation.
Foods and Supplements That Mimic Blood
Before assuming the worst, consider what you’ve eaten in the past day or two. Beets, red gelatin, tomato soup, and red food dye can all turn stool red in a way that looks convincingly like blood. Iron supplements and bismuth-based stomach medications (the active ingredient in Pepto-Bismol) can turn stool black, mimicking the tarry appearance of upper GI bleeding. If you recently consumed any of these and feel otherwise fine, waiting a day to see if the color returns to normal is reasonable.
When Blood in Stool Is Urgent
A small amount of bright red blood on the toilet paper after straining, with no other symptoms, is the scenario least likely to be dangerous. But certain combinations of symptoms signal that something more serious is happening and you should seek care quickly:
- Lightheadedness or feeling faint, which can indicate significant blood loss
- Chest pain or shortness of breath
- Abdominal, pelvic, or rectal pain that is new or severe
- Fever alongside bloody stool, suggesting infection or active inflammation
- Nausea, vomiting, or vomiting blood
- Difficulty swallowing or jaundice (yellowing of the skin or eyes)
- Unexplained weight loss over weeks or months
Heavy bleeding that doesn’t stop, or large clots passing with stool, also warrants an emergency visit regardless of other symptoms.
How Doctors Find the Cause
If you report blood in your stool, the first step is often a physical exam and a discussion of your symptoms, medications, and family history. For bleeding that isn’t clearly from a visible hemorrhoid or fissure, doctors typically move to a colonoscopy, which uses a flexible camera to examine the entire colon and can both identify the source of bleeding and treat certain causes on the spot, like removing a polyp or cauterizing a bleeding vessel.
There are also stool-based tests that check for hidden blood you can’t see with the naked eye. A fecal immunochemical test (FIT) detects blood proteins in a stool sample and is commonly used as a screening tool. It’s important to know that these tests can confirm blood is present but can’t tell you why. A positive result almost always leads to a colonoscopy for a definitive answer. Other options include a stool DNA test that looks for genetic markers of polyps or cancer, a sigmoidoscopy that examines only the lower colon, or a CT-based virtual colonoscopy.
The Colorectal Cancer Connection
Blood in the stool is one possible symptom of colorectal cancer, which is why it understandably causes anxiety. It’s worth keeping in perspective that cancer is far less common than hemorrhoids or fissures as a cause. Still, colorectal cancer is one of the most preventable cancers when caught early through screening.
The U.S. Preventive Services Task Force recommends that all adults begin routine colorectal cancer screening at age 45 and continue through age 75. This applies to people at average risk with no symptoms. If you have a family history of colorectal cancer or polyps, screening may need to start earlier. Blood in the stool before age 45, especially if it’s persistent, dark, or accompanied by weight loss or changing bowel habits, still deserves a medical evaluation regardless of screening guidelines.