Blood in your stool is usually caused by something minor and treatable, like hemorrhoids or a small tear in the skin around your anus. But the color, amount, and accompanying symptoms all matter, because they point to different parts of your digestive tract and different levels of urgency. Understanding what you’re seeing can help you figure out whether this is a common nuisance or something that needs prompt attention.
What the Color Tells You
The color of the blood is the single most useful clue. Bright red blood typically comes from the lower digestive tract: the rectum, anus, or the end of the colon. Dark red or maroon blood usually originates higher up in the colon. Black, tarry stool with a foul smell signals bleeding in the upper digestive tract, meaning the stomach, esophagus, or the first section of the small intestine. Blood from the upper tract turns black because it gets partially digested on the way down.
Before you panic, consider what you’ve eaten or taken recently. Beets, red gelatin, red-dyed snack foods, fruit punch, and red licorice can all make stool look bright red. On the dark side, iron supplements, bismuth-based stomach medicines (like Pepto-Bismol), activated charcoal, blueberries, and large amounts of dark leafy greens like spinach or kale can turn stool black. If any of these apply, wait a day or two after stopping the food or supplement and see if the color returns to normal.
Hemorrhoids and Anal Fissures
These are the two most common reasons people see bright red blood on toilet paper, on the surface of stool, or dripping into the bowl. Hemorrhoids are inflamed blood vessels in or just outside the anus. They often cause painless bleeding, though external hemorrhoids can itch or ache. Straining during bowel movements, sitting for long periods, pregnancy, and chronic constipation all increase your risk.
Anal fissures are small tears in the lining of the anus. They cause bright red bleeding during or after a bowel movement, and the key difference from hemorrhoids is pain: fissures typically produce a sharp, stinging sensation during the bowel movement that can linger afterward. You may even be able to see the tear. Hard or large stools are the usual culprit. Most fissures heal on their own within a few weeks with increased fiber, more water, and stool softeners.
Diverticular Bleeding
Diverticula are small pouches that form in weak spots along the colon wall, and they become increasingly common after age 40. Most people with diverticula never have symptoms, but sometimes a blood vessel stretched across one of these pouches ruptures. The result is an abrupt onset of painless rectal bleeding, often bright red to dark maroon, sometimes mixed with clots. It can look alarming because the volume can be significant, but roughly 75 to 80 percent of diverticular bleeds stop on their own. If the bleeding is heavy or doesn’t slow down, it requires medical evaluation.
Peptic Ulcers and Upper GI Bleeding
Peptic ulcers are the most common cause of acute upper gastrointestinal bleeding. These are open sores in the stomach lining or the upper part of the small intestine, often caused by a bacterial infection or long-term use of anti-inflammatory painkillers. When an ulcer bleeds, the blood is digested as it travels through the intestines, producing black, tarry stool with a distinctly foul odor. You won’t see red blood in this case. Upper GI bleeding can also come from tears in the esophagus or inflamed stomach lining.
Black, tarry stool that you can’t explain with iron supplements, bismuth medications, or dark foods is a reason to seek medical attention promptly. It means you’re losing blood from somewhere above the intestine, and the cause needs to be identified.
Colorectal Cancer and Polyps
This is what most people are really worried about when they search this question. Colorectal cancer can cause blood in the stool, but it’s far less common than hemorrhoids or fissures, especially in younger adults. Polyps, which are small growths on the colon lining that can eventually become cancerous, may also bleed. The blood from polyps or tumors is sometimes visible but is often microscopic, meaning you wouldn’t notice it without a lab test.
Warning signs that raise the possibility of something more serious include a persistent change in your bowel habits (new constipation, diarrhea, or narrower stools lasting more than a few weeks), unintentional weight loss, fatigue that doesn’t improve with rest, and a feeling that your bowel doesn’t empty completely. Blood in the stool combined with any of these deserves a thorough workup. The U.S. Preventive Services Task Force recommends that all adults begin routine colorectal cancer screening at age 45, even without symptoms.
How Doctors Find the Source
If you have visible blood in your stool or symptoms like pain, a change in bowel habits, or ongoing diarrhea, your doctor will likely move beyond basic screening tests and evaluate you directly. The most thorough option is a colonoscopy, in which a flexible tube with a camera is guided through the entire colon and rectum. The procedure takes 30 to 60 minutes, requires sedation, and involves a bowel prep the day before (a liquid diet and a cleansing solution). During the exam, the doctor can remove polyps and take tissue samples on the spot, which is its main advantage over other tests.
For situations where a less invasive first step makes sense, stool-based tests can detect hidden blood or abnormal DNA shed by precancerous cells. These can be done at home with no prep or sedation. A fecal immunochemical test checks for hidden blood and is typically repeated every year. A stool DNA test looks for both blood and genetic changes associated with cancer or precancerous growths and is repeated every three years. If either test comes back positive, a colonoscopy is the next step to get a direct look.
When It’s an Emergency
Most rectal bleeding is not an emergency, but some situations require immediate help. Call 911 or get to an emergency room if you experience any of the following alongside rectal bleeding: 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 are signs of shock, meaning your body is losing blood faster than it can compensate.
You should also seek urgent care if the bleeding is continuous or heavy, or if it comes with severe abdominal pain or cramping. A single episode of a small amount of bright red blood on the toilet paper, with no other symptoms, is far less concerning and can usually wait for a scheduled appointment.