Blood in your stool is always worth paying attention to, but it’s not always a sign of something serious. The most common causes are hemorrhoids and small tears in the skin around the anus, both of which are benign and treatable. That said, rectal bleeding can also signal conditions that need medical evaluation, including inflammatory bowel disease and colorectal cancer. The color of the blood, the amount, and your other symptoms all help determine what’s going on.
What the Color Tells You
The shade of blood you see gives a rough map of where the bleeding is coming from. Bright red blood typically originates in the lower part of your digestive tract, usually the colon, rectum, or anus. It’s fresh, hasn’t traveled far, and often shows up on toilet paper or in the bowl after a bowel movement.
Dark red or maroon blood usually comes from higher up in the colon or the lower part of the small intestine. Black, tarry stool, known medically as melena, points to bleeding in the stomach or upper small intestine. Digestive chemicals break down the blood as it travels through your system, turning it dark and giving it a sticky, tar-like texture. If your stool looks black and has a strong, unusually foul smell, that combination is more concerning than color alone.
The Most Common (and Least Serious) Causes
Hemorrhoids are the leading cause of bright red rectal bleeding. They’re swollen blood vessels in the rectum or around the anus, and most of them don’t even hurt. You might notice blood on the toilet paper, a few drops in the bowl, or a feeling of fullness or itching around the anus. Internal hemorrhoids, which sit inside the rectum, tend to bleed more but cause less discomfort than external ones.
Anal fissures are small tears in the lining of the anus, usually caused by passing hard or large stools. Unlike hemorrhoids, fissures typically cause a sharp, stinging pain during bowel movements that can linger afterward. You may also notice itching or burning that persists between trips to the bathroom. Both hemorrhoids and fissures generally heal on their own or with simple at-home care like increasing fiber intake and staying hydrated.
When Blood in Stool Points to Something Bigger
Inflammatory bowel disease, which includes ulcerative colitis and Crohn’s disease, can cause blood in your stool along with persistent diarrhea, abdominal cramping, and fatigue. The bleeding in these conditions comes from inflamed or ulcerated tissue in the intestinal lining. Most cases involve small amounts of blood mixed into the stool rather than dramatic bleeding. Major hemorrhage from IBD is actually uncommon, occurring in roughly 0.1% of ulcerative colitis cases and about 1.2% of Crohn’s disease cases.
Colorectal cancer is the concern most people are really searching about when they type this question. A study published by the American College of Surgeons found that in adults under 50, rectal bleeding was the single strongest predictor of colorectal cancer, increasing the odds of diagnosis by 8.5 times compared to patients without bleeding. That sounds alarming, but context matters: the baseline risk in younger adults is low, so even an 8.5-fold increase still means the vast majority of people with rectal bleeding do not have cancer. Still, it’s the reason any unexplained or persistent rectal bleeding deserves a medical evaluation, especially if you also have changes in bowel habits, unintended weight loss, or a feeling that your bowel doesn’t empty completely.
Medications That Cause GI Bleeding
Over-the-counter painkillers like ibuprofen, naproxen, and aspirin are among the most common medication-related causes of gastrointestinal bleeding. These drugs irritate the stomach lining and reduce the ability of blood to clot at the site of irritation. Research shows NSAIDs more than double the risk of bleeding from weak spots in the colon wall.
The risk climbs significantly if you also take a blood thinner. People on warfarin who also use NSAIDs have roughly 2.7 times the risk of GI bleeding compared to those on warfarin alone. Newer blood thinners carry a similar pattern: combining them with anti-inflammatory painkillers approximately doubles the chance of GI bleeding. If you take any blood-thinning medication, even occasional use of ibuprofen or naproxen is worth discussing with your doctor.
Foods That Mimic Blood
Before you panic, consider what you’ve eaten in the last day or two. Beets are the classic culprit, turning stool (and urine) a startling red. Red gelatin, tomato soup, red food dyes in candy or drinks, and even large amounts of cranberries can do the same. On the darker end, iron supplements, bismuth-based stomach medicines like Pepto-Bismol, and black licorice can all turn stool dark enough to look like melena. If you suspect a food is the cause, the color change typically resolves within a day or two of avoiding that food.
Red meat, raw fruits, and certain vegetables like radishes and horseradish can also interfere with fecal blood tests, producing false positive results. If you’re preparing for a stool-based screening test, you’ll typically be asked to avoid these foods for 48 hours beforehand.
How Bleeding Is Investigated
Your doctor’s approach depends on your age, symptoms, and risk factors. A fecal immunochemical test (FIT) is a simple at-home stool test that detects hidden blood you can’t see with the naked eye. It’s inexpensive, noninvasive, and widely used for routine screening. A colonoscopy is more thorough: it lets a doctor visually examine the entire colon, remove precancerous polyps on the spot, and take tissue samples if anything looks abnormal. Studies show colonoscopy prevents more than 80% of left-sided colon cancers and over half of right-sided cancers through polyp removal. A single normal colonoscopy provides reassurance that may last 10 to 15 years or even longer.
The U.S. Preventive Services Task Force recommends that most adults begin routine colorectal cancer screening at age 45 and continue through age 75. People with higher risk factors, such as a family history of colorectal cancer, may need to start earlier.
Signs That Need Immediate Attention
Most rectal bleeding is not an emergency, but certain combinations of symptoms are. Heavy or continuous bleeding that doesn’t stop, especially if it fills the toilet bowl or soaks through clothing, warrants a trip to the emergency room. The same is true if bleeding comes with severe abdominal pain or cramping.
Call 911 if you notice rectal bleeding alongside any signs that your body isn’t circulating blood well: rapid, shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These symptoms suggest significant blood loss and need immediate treatment.
A small streak of bright red blood on the toilet paper after a hard bowel movement is, on its own, rarely dangerous. But bleeding that recurs over weeks, appears without an obvious cause, or accompanies other digestive symptoms is your body’s way of telling you something needs a closer look.