Blood in your stool is surprisingly common, affecting roughly 1 in 6 adults in the United States, and the cause is usually something treatable like hemorrhoids or a small tear in the skin around your anus. That said, rectal bleeding can also signal conditions that need medical attention, from inflammatory bowel disease to colorectal cancer. The color of the blood, the amount, and whether you have other symptoms all help narrow down what’s going on.
What the Color of the Blood Tells You
The single most useful clue is whether the blood is bright red or dark and tarry. Bright red blood typically comes from the lower part of your digestive tract, meaning your rectum or colon. You might see it on the toilet paper, in the bowl, or coating the surface of your stool. This type of bleeding is more likely tied to hemorrhoids, fissures, or conditions affecting the colon itself.
Dark, black, tarry stool points to bleeding higher up in the digestive tract, such as the stomach or small intestine. Blood that travels through the full length of your gut gets digested along the way, which turns it black and gives it a sticky, tar-like consistency. This kind of stool has a distinct, unusually strong odor that’s hard to miss.
Before you panic about either color, consider what you’ve eaten or taken recently. Iron supplements, Pepto-Bismol, activated charcoal, black licorice, and blueberries can all turn your stool black. Beets and foods with red dye can make stool look reddish even though no blood is present.
Hemorrhoids: The Most Common Cause
Hemorrhoids are swollen blood vessels in or around the rectum, and they’re the leading reason people notice blood after a bowel movement. Internal hemorrhoids, the kind inside the rectum, often bleed painlessly. You’ll see bright red blood on the paper or dripping into the toilet, but you may not feel anything unusual. External hemorrhoids, located around the outside of the anus, are more likely to cause itching or mild discomfort but can also bleed.
Straining during bowel movements, sitting on the toilet for long periods, chronic constipation, and pregnancy all increase your risk. Most hemorrhoids improve on their own with more fiber, more water, and less time straining. A doctor can usually diagnose them with a physical exam.
Anal Fissures: Small Tears, Sharp Pain
An anal fissure is a small tear in the lining of the anus, and it’s the other very common explanation for blood in your stool. The key difference from hemorrhoids is pain. Fissures tend to cause a sharp, stinging sensation during and sometimes after a bowel movement. You’ll typically see a small amount of bright red blood on the toilet paper.
Fissures often develop from passing a hard or unusually large stool. They can also result from chronic diarrhea or inflammation. Most heal within a few weeks with stool softeners and warm baths, though deeper or recurring fissures sometimes need further treatment.
Inflammatory Bowel Disease
If your bleeding comes with persistent diarrhea, abdominal pain, fatigue, or unexplained weight loss, inflammatory bowel disease (IBD) is a possibility worth investigating. The two main forms are ulcerative colitis and Crohn’s disease. Both can cause rectal bleeding, but they behave differently.
Ulcerative colitis affects the colon and rectum and frequently causes bloody diarrhea as one of its hallmark symptoms. Blood is often mixed into the stool rather than just sitting on the surface. Crohn’s disease can affect any part of the digestive tract and causes diarrhea that may or may not be bloody. Both conditions tend to flare and then improve in cycles. If you’re having weeks of diarrhea with blood, cramping, and fatigue, these are conditions a gastroenterologist would want to evaluate.
Diverticular Bleeding
Diverticula are small pouches that form in the wall of the colon, usually in people over 40. They’re extremely common and usually cause no problems at all. But occasionally, a blood vessel running along the wall of one of these pouches can rupture and bleed.
What makes diverticular bleeding distinctive is that it tends to be sudden, painless, and heavy. You may pass a large amount of dark red or maroon-colored blood with little warning. It can be alarming, but most episodes stop on their own. Heavy bleeding that causes dizziness when you stand up, rapid breathing, or a feeling like you might faint is a sign of significant blood loss and requires emergency care.
Colorectal Cancer and Polyps
This is the possibility most people are worried about when they search this question, and it deserves a straightforward answer. Colorectal cancer can cause blood in the stool, but it’s far less common than hemorrhoids or fissures as a cause of rectal bleeding.
In early stages, colon cancer often produces no noticeable stool changes at all. When it does cause bleeding, it may be a small amount that’s invisible to the naked eye, detectable only through screening tests. As cancer grows, it can cause visible blood (bright red from the lower colon, darker from higher up), along with other changes: stools that become persistently thinner or pencil-shaped, a lasting change in how often you go, increased mucus in your stool, or a feeling that your bowel doesn’t fully empty.
Precancerous polyps, which are growths on the inner lining of the colon, can also bleed intermittently. Finding and removing these polyps early is the entire purpose of routine colonoscopy screening. If you’re over 45, or younger with a family history of colorectal cancer, and you haven’t been screened, rectal bleeding is a strong reason to get that done.
Other Possible Causes
Several less common conditions can also cause blood in your stool. Infections from bacteria like Salmonella, E. coli, or Campylobacter can inflame the gut lining and cause bloody diarrhea, usually alongside cramping, fever, and nausea. These typically develop after contaminated food or water exposure and resolve within days to a couple of weeks.
Stomach ulcers or inflammation in the upper digestive tract can produce black, tarry stools. Blood thinners and anti-inflammatory medications like aspirin and ibuprofen raise the risk of bleeding anywhere in the digestive tract, especially with regular use.
Signs That Need Immediate Attention
A small amount of bright red blood on the toilet paper after straining is worth mentioning to your doctor, but it rarely requires a trip to the emergency room. What does require urgent care is any combination of rectal bleeding with these symptoms:
- Dizziness or lightheadedness when standing
- Rapid, shallow breathing
- Fainting or confusion
- Cold, clammy, or pale skin
- Blurred vision
- Nausea with heavy bleeding
These are signs of significant blood loss and possible shock. A large, sudden bleed from a diverticulum or ulcer can cause this, and it needs emergency treatment. Even without those dramatic symptoms, rectal bleeding that keeps recurring over weeks, bleeding that’s mixed into your stool rather than just on the surface, or any bleeding paired with weight loss, persistent changes in bowel habits, or fatigue warrants a prompt medical evaluation. The goal isn’t to assume the worst. It’s to confirm the likeliest, most benign explanation and rule out the rest.