Blood in your stool is common, affecting roughly 13% to 34% of the general population at some point, and the cause is usually not serious. Hemorrhoids and small tears in the skin around the anus account for the majority of cases. That said, the color of the blood, the amount, and any symptoms that come with it all matter, because they point to different parts of your digestive tract and different underlying problems.
What the Color of the Blood Tells You
The color is your single best clue to where the bleeding is coming from. Bright red blood, whether on the toilet paper, dripping into the bowl, or coating the surface of your stool, typically originates in the lower digestive tract: the colon, rectum, or anus. This is the most common type people notice, and it often traces back to hemorrhoids or a small anal tear.
Dark red or maroon-colored blood mixed into the stool usually points to bleeding higher up in the colon or in the small intestine. Black, tarry, sticky stool with a distinctly foul smell signals bleeding even farther upstream, often from the stomach or upper small intestine. Blood turns black as it travels through the digestive tract and gets broken down by stomach acid and enzymes. Occasionally, a very fast bleed from the stomach can move through quickly enough to still appear bright red when it exits, though this is less common and usually involves a large volume of blood.
One important caveat: certain foods and medications change stool color in ways that look alarming but aren’t bleeding at all. Beets and red food coloring can make stool appear reddish. Iron supplements, bismuth-containing antacids (like Pepto-Bismol), black licorice, blueberries, and activated charcoal can all turn stool black. If you’ve consumed any of these recently, that may explain what you’re seeing. A simple chemical test at your doctor’s office can confirm whether actual blood is present.
The Most Common Causes
Hemorrhoids
Hemorrhoids are the most common cause of rectal bleeding in middle-aged and older adults. They’re swollen blood vessels in or around the rectum that can bleed when you strain during a bowel movement. Internal hemorrhoids, the ones inside the rectum, usually don’t hurt. You’ll see bright red blood on the toilet paper or in the bowl, but the act of going to the bathroom itself feels normal. External hemorrhoids, by contrast, can itch, swell, and cause mild pain.
Anal Fissures
An anal fissure is a small tear in the lining of the anus, often caused by passing a hard or large stool. The hallmark of a fissure is sharp pain during and sometimes after a bowel movement, along with streaks of bright red blood on the stool or on the toilet paper. If the bleeding comes with a stinging or tearing sensation right at the opening, a fissure is a likely explanation. Most heal on their own within a few weeks with softer stools and good hygiene.
Diverticular Bleeding
Diverticula are small pouches that form in the wall of the colon, most often in people over 40. They’re extremely common and usually harmless. But the blood vessels in these pouches can become fragile over time and rupture, causing sudden, painless bleeding that’s often significant in volume. The blood is typically dark red or maroon. Diverticular bleeds usually stop on their own, but the amount of blood can be startling enough to send people to the emergency room.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease are chronic conditions where the immune system attacks the lining of the digestive tract, causing inflammation, pain, and bleeding. Ulcerative colitis is more closely associated with bloody diarrhea, often accompanied by cramping in the lower abdomen, an urgent need to use the bathroom, and a frustrating feeling that you haven’t fully emptied your bowels even after going. Crohn’s disease more often causes abdominal pain with nonbloody diarrhea and weight loss, though bleeding can occur depending on where the inflammation is located.
Infections
Bacterial infections from organisms like E. coli and C. difficile can cause bloody diarrhea that comes on suddenly. Sexually transmitted infections affecting the rectum, including gonorrhea, chlamydia, and herpes, can also cause rectal bleeding. These infections typically come with other symptoms like fever, cramping, or discharge.
How Likely Is It to Be Cancer?
This is the question most people are really asking when they search for blood in their stool, so here are the numbers. In a study of 604 patients who went to a doctor specifically for rectal bleeding, 3.6% were diagnosed with colorectal cancer. That means more than 96% had something else.
Age is the strongest predictor. Among patients under 50, only 1.1% had cancer. Between ages 50 and 69, that number rose to 4.8%. For those 70 and older, it was 7.5%. People over 70 were roughly eight times more likely to have cancer than those under 50. So while cancer is always worth ruling out, the odds are heavily in your favor, especially if you’re younger.
The U.S. Preventive Services Task Force recommends routine colorectal cancer screening starting at age 45 for people at average risk. If you’re 45 or older and haven’t been screened, rectal bleeding is a good reason to get that process started. If you’re younger but have a family history of colorectal cancer or inflammatory bowel disease, screening may be appropriate earlier.
Signs That Need Urgent Attention
Most rectal bleeding doesn’t require a trip to the emergency room. But a few situations do. Large amounts of blood, whether bright red or dark, that don’t stop after a few minutes need immediate evaluation. Blood mixed with dizziness, lightheadedness, or fainting suggests you’re losing enough blood to affect your circulation.
Severe bleeding can, in rare cases, lead to shock. Signs of shock include confusion or loss of consciousness, a racing heart rate, pale skin, cold hands and feet, and heavy sweating. This is a medical emergency. Other symptoms that warrant a prompt call to your doctor, even if they don’t require the ER, include abdominal pain or cramping alongside the bleeding, shortness of breath, and unusual fatigue.
Only about 40% of people who experience rectal bleeding actually seek medical care. Many assume it’s hemorrhoids and move on. That’s often correct, but it means a significant number of people with treatable conditions go undiagnosed longer than necessary.
What to Track Before Your Appointment
If you decide to see a doctor, and you should if the bleeding is new, recurring, or accompanied by other symptoms, keeping a few details in mind will make the visit more productive. Note the color of the blood: bright red, dark red, or black. Pay attention to where you see it: on the toilet paper only, in the bowl, mixed into the stool, or coating its surface. Track how often it happens and roughly how much blood there is each time.
Also note any associated symptoms. Does it hurt when you go? Are your bowel habits changing, with new constipation or diarrhea? Have you lost weight without trying? Are you more tired than usual? These details help narrow the possible causes quickly. Your doctor can perform a physical exam, and if needed, order a stool test that checks for hidden blood or schedule a closer look at the colon with a scope.
Stool Tests for Hidden Blood
Sometimes blood in the stool isn’t visible to the naked eye. Screening stool tests can detect microscopic amounts. The two main types are the older guaiac-based test and the newer immunochemical test, sometimes called a FIT. Both check for blood, but they work differently. The immunochemical test is more accurate, correctly identifying people without serious disease about 92% of the time, compared to 76% for the older test. This means fewer false alarms. Their ability to detect actual disease is similar, around 29% to 36%, which is why these tests are used as a first step, not a final answer. A positive result on either test leads to a colonoscopy for a definitive look.