Blood in your stool usually comes from somewhere in your digestive tract, and in most cases the cause is something common and treatable, like hemorrhoids or a small tear in the skin around your anus. That said, the color, amount, and any symptoms alongside the bleeding all matter in figuring out what’s going on.
What the Color of the Blood Tells You
Bright red blood typically comes from the lower part of your digestive tract: the rectum, anus, or the end of the large intestine. Because it hasn’t traveled far, it still looks red when it shows up on toilet paper, in the bowl, or on the surface of your stool.
Dark, tarry, almost black stool points to bleeding higher up, in the stomach or small intestine. Blood that travels the full length of your gut gets broken down by digestive enzymes along the way, which turns it dark. If your stool looks like black tar and has a strong, unusual smell, the source is likely well above the colon.
Hemorrhoids
Hemorrhoids are the single most common reason people see bright red blood after a bowel movement. They’re swollen blood vessels inside the rectum or around the anus, and they bleed easily when stool passes over them. Internal hemorrhoids, the ones inside the rectum, usually don’t hurt at all. You might not even know they’re there until you notice blood on the paper or in the toilet. External hemorrhoids, closer to the surface, can itch or feel uncomfortable but are still rarely a cause for serious concern.
Straining during bowel movements, sitting on the toilet for long periods, chronic constipation, and pregnancy all increase your chances of developing them. Eating more fiber, drinking enough water, and avoiding straining usually shrinks them over time.
Anal Fissures
An anal fissure is a small tear in the lining of the anus. Unlike hemorrhoids, fissures tend to hurt, sometimes sharply, especially during and right after you poop. You may also notice itching or burning that lingers. The blood is usually bright red and in small amounts.
Fissures commonly happen when you pass a hard or unusually large stool. They can also result from chronic diarrhea or straining. Most heal on their own within a few weeks if you keep your stool soft with fiber and plenty of fluids.
Diverticular Bleeding
Diverticula are small pouches that form along the walls of the colon, most often in people over 40. They’re extremely common and usually harmless. Occasionally, though, a blood vessel near one of these pouches bursts, and the result can be dramatic: a sudden, painless gush of bright red or maroon blood. Diverticular bleeding accounts for 30 to 50 percent of all cases of large-volume rectal bleeding, making it the most common cause of heavy bleeding from the lower digestive tract.
The key feature is that it’s painless. There’s no cramping, no straining beforehand. It just happens. Most episodes stop on their own, but the volume of blood can be alarming enough to warrant a trip to the emergency room.
Inflammatory Bowel Disease
If the bleeding comes with ongoing diarrhea, abdominal cramping, urgency, fatigue, or unexplained weight loss, the cause may be an inflammatory condition like ulcerative colitis or Crohn’s disease. Ulcerative colitis in particular causes bloody diarrhea, often mixed with mucus or pus. When the inflammation affects the entire colon, episodes can be severe and include fever and significant weight loss.
These conditions are chronic, meaning they involve flare-ups and remission periods over time. They’re not something you’d develop overnight. If you’ve had weeks of bloody, loose stools along with belly pain and fatigue, that pattern is worth getting evaluated.
Medications That Increase Bleeding Risk
Certain common medications can make your gut more likely to bleed. Anti-inflammatory painkillers like ibuprofen, naproxen, and aspirin are strongly associated with both upper and lower gastrointestinal bleeding. Research shows that regular NSAID use roughly doubles the risk of bleeding from diverticula in the colon.
Blood thinners raise the stakes further. Taking a blood thinner like warfarin alongside an NSAID nearly triples the risk of gastrointestinal bleeding compared to taking the blood thinner alone. Even newer blood thinners carry elevated risk when combined with anti-inflammatory painkillers. If you’re on any of these medications and notice blood in your stool, that combination is important information for your doctor.
Could It Be Colorectal Cancer?
This is the fear most people have when they search this question, so here are the numbers. In a study of patients aged 45 and older who showed up at a primary care office with new rectal bleeding, about 6 percent were ultimately diagnosed with colorectal cancer. The rate was highest in people 65 to 74 (about 9.5 percent) and lowest in the 55 to 64 age group (around 1.3 percent). For people under 45, the odds are even lower, though not zero.
Colorectal cancer tends to come with other clues: a persistent change in bowel habits lasting weeks, unexplained weight loss, a feeling that your bowel doesn’t fully empty, or new fatigue. A single episode of bright red blood on the toilet paper in an otherwise healthy young person is far more likely to be a hemorrhoid or fissure. But rectal bleeding that keeps coming back, especially if you’re over 45 or have a family history of colon cancer, is a reason to get checked.
What Happens When You Get It Checked
Your doctor will start with your medical history, a physical exam, and often a rectal exam. From there, the path depends on your age, symptoms, and risk factors.
- Stool tests can detect hidden blood you might not see, which helps establish whether bleeding is ongoing.
- Blood tests check for anemia (low red blood cell counts from chronic blood loss) and how well your blood is clotting.
- Colonoscopy is the most thorough tool. A flexible camera examines the entire large intestine and rectum, and it can both find the source of bleeding and treat certain problems on the spot, like removing polyps.
- Flexible sigmoidoscopy looks at just the lower portion of the colon and rectum, which is sometimes enough when the bleeding is clearly coming from that area.
- Capsule endoscopy involves swallowing a tiny camera in a pill-sized capsule that photographs your digestive tract as it passes through. This is used when bleeding seems to come from the small intestine, which is hard to reach with standard scopes.
For most people, especially those under 40 with a clear pattern matching hemorrhoids or a fissure, a physical exam and conversation may be all that’s needed. A colonoscopy becomes more important when bleeding is unexplained, recurrent, or accompanied by warning signs like weight loss or a change in bowel habits.
Signs You Need Emergency Help
Most rectal bleeding is not an emergency, but large-volume bleeding can become one. Call emergency services or get to an ER if you’re passing a significant amount of blood and experience any of the following: dizziness or lightheadedness when you stand up, rapid or shallow breathing, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very little urine output. These are signs your body is losing blood faster than it can compensate, and that requires immediate care.