Blood in your stool most often comes from hemorrhoids or a small tear in the lining of your anus, but it can also signal conditions ranging from inflammatory bowel disease to colorectal cancer. The color of the blood is one of the most useful clues to what’s going on: bright red blood typically means the source is near the end of your digestive tract (rectum or anus), while dark, tarry, or black stool suggests bleeding higher up, such as the stomach or small intestine.
Hemorrhoids: The Most Common Cause
Hemorrhoids are swollen veins in or around your rectum and anus, and they’re by far the most frequent reason people see blood after a bowel movement. The blood is usually bright red and shows up on toilet paper, on the surface of the stool, or dripping into the bowl. Hemorrhoids tend to cause an achy, itchy discomfort that comes and goes rather than sharp pain. Straining during bowel movements, sitting for long periods, pregnancy, and chronic constipation all make them more likely.
Most hemorrhoids respond to simple home care: over-the-counter medicated creams, warm sitz baths, and adding fiber to your diet to soften stools so you strain less. Bleeding from hemorrhoids can look alarming because of the amount, sometimes producing noticeable clots, but it typically stops on its own within a few days once the irritation settles down.
Anal Fissures: Small Tears, Sharp Pain
An anal fissure is a tiny tear in the lining of the anus, usually caused by passing a hard or large stool. The hallmark difference from hemorrhoids is pain. Fissures produce an intense, sharp, burning pain that can last for hours after a bowel movement, while hemorrhoids rarely hurt that much. Fissures tend to produce smaller amounts of bright red blood compared to hemorrhoids, often just a streak on the toilet paper.
Fissures heal on their own in most cases, especially if you keep stools soft with fiber and plenty of water. Chronic fissures that don’t heal after several weeks sometimes need medical treatment.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease, the two main forms of inflammatory bowel disease (IBD), both cause rectal bleeding. Ulcerative colitis is especially associated with blood or mucus in the stool, along with cramping abdominal pain and frequent, urgent trips to the bathroom. The bleeding tends to be ongoing rather than a one-time event, and it often comes with diarrhea that persists for weeks.
If you’re seeing blood in your stool alongside persistent changes in bowel habits, cramping, fatigue, or unintended weight loss, IBD is one of the conditions your doctor will want to rule out. It’s a chronic condition, but treatments can control symptoms and reduce flare-ups significantly.
Diverticular Bleeding
Diverticula are small pouches that form in the walls of the colon, most commonly in people over 40. They’re usually harmless, but when one of these pouches bleeds, it can produce a sudden, painless gush of dark red or maroon blood. Diverticular bleeding often stops on its own but can be heavy enough to be frightening. When these pouches become infected or inflamed (diverticulitis), the picture changes: you’ll typically have severe, sudden abdominal pain, often on the lower left side, that may be constant or come in waves.
Colorectal Cancer and Polyps
Colorectal cancer is a less common but serious cause of blood in the stool. Precancerous growths called polyps can also bleed. The blood may be bright red or dark, and sometimes it’s invisible to the naked eye, detectable only through lab testing. What makes colorectal bleeding harder to catch is that it’s often subtle, mixed into the stool rather than visible on the surface.
Rates of colorectal cancer in people under 50 have been climbing in recent years. A study published in The Lancet Oncology found that early-onset colorectal cancer increased in 27 countries over the most recent decade analyzed. The sharpest annual increases were in New Zealand, Chile, Puerto Rico, and England. This trend is one reason screening recommendations have shifted to start at age 45 in many guidelines. Blood in your stool that persists, especially alongside unexplained weight loss, a change in bowel habits, or a feeling that your bowel doesn’t fully empty, warrants a colonoscopy regardless of your age.
What the Color Tells You
Bright red blood on the toilet paper or coating the stool points to a source near the anus or lower rectum, such as hemorrhoids, fissures, or rectal polyps. Dark red or maroon blood mixed into the stool suggests a source further up in the colon, like diverticular bleeding or a colon polyp. Black, tarry stool with a distinctly foul smell (called melena) indicates bleeding in the stomach or upper small intestine, because the blood has been partially digested during its transit through the gut. This type of stool warrants prompt medical attention.
Foods and Medications That Mimic Blood
Before you panic, consider what you’ve eaten or taken recently. Beets can turn stool a startling red that looks a lot like blood. Foods with dark blue or black food coloring can make stool appear black. Iron supplements and bismuth-containing medications like Pepto-Bismol also turn stool black, which can be mistaken for the tarry appearance of upper GI bleeding. If your stool looks unusual but you recently consumed any of these, wait a day or two and see if the color returns to normal.
How Rectal Bleeding Is Diagnosed
When you report blood in your stool, doctors typically start with a physical exam and a discussion of your symptoms: how much blood, what color, how long it’s been happening, and whether you have pain. For minor, one-time bleeding in a young person with obvious hemorrhoid symptoms, this may be enough. For anything persistent, heavy, or accompanied by other symptoms, a colonoscopy is the standard next step. This procedure lets a doctor visually inspect the entire lining of your colon and rectum, take tissue samples, and even remove polyps on the spot.
If bleeding is heavy and active, doctors may use a CT scan with contrast dye to locate exactly where the blood is coming from before deciding on treatment. This is typically reserved for situations where someone is losing enough blood to affect their blood pressure or heart rate.
Signs That Need Emergency Attention
Most rectal bleeding is not an emergency, but some situations require immediate help. Call 911 or get to an emergency room if you have significant rectal bleeding along with any of these signs: rapid or shallow breathing, dizziness or lightheadedness when you stand up, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These suggest you’re losing enough blood to go into shock.
You should also get to an emergency room if the bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping. Even without those dramatic symptoms, blood in your stool that shows up repeatedly over days or weeks is worth a call to your doctor to determine the cause.