Bloody stool is surprisingly common. Roughly one in seven adults has experienced rectal bleeding, and the rate is actually higher in younger people than older ones. The causes range from something as minor as a small tear near the anus to serious conditions like inflammatory bowel disease or colorectal cancer. The color of the blood is one of the most useful clues to where it’s coming from.
What the Color of the Blood Tells You
Bright red blood typically comes from the lower digestive tract: the colon, rectum, or anus. You might see it on toilet paper, dripping into the bowl, or mixed into the stool. Because the blood hasn’t traveled far, it stays red.
Black, tarry stool points to bleeding higher up, usually in the stomach or esophagus. Blood that travels the full length of the digestive tract gets broken down along the way, turning dark and sticky. This type of stool often has a distinctly foul smell that’s different from normal. If you’re seeing black stools, the source is generally more urgent to identify because upper GI bleeds can involve significant blood loss before you notice anything visually.
Hemorrhoids and Anal Fissures
These two are the most common causes of bright red blood on toilet paper, and they’re often confused with each other. Hemorrhoids are swollen veins in the rectum or around the anus, similar to varicose veins. Internal hemorrhoids tend to bleed painlessly. You notice bright red blood on the tissue or in the bowl, but nothing hurts. External hemorrhoids can cause a dull ache, pressure, or throbbing that lasts throughout the day. If a blood clot forms inside one (a thrombosed hemorrhoid), the pain can become sudden and severe.
Anal fissures are small tears in the thin lining of the anus, usually caused by passing hard or large stools. The pain is sharp and searing during a bowel movement, sometimes described as feeling like passing shards of glass. That intense pain can linger as a deep ache for minutes to hours afterward. Like hemorrhoids, fissures produce bright red blood on toilet paper, but the pain is the distinguishing feature. Fissures are generally more acutely painful than hemorrhoids.
Diverticular Bleeding
Diverticulosis, where small pouches form in the colon wall, is extremely common in adults over 50. Most people with diverticula never know they have them. But occasionally, a blood vessel near one of these pouches weakens and ruptures, producing a sudden, sometimes alarming amount of bright red or maroon blood. The bleeding is typically painless, which catches people off guard. It often stops on its own, but the volume alone can be enough to warrant emergency evaluation. When the pouches become infected or inflamed, the condition is called diverticulitis, which adds abdominal pain, fever, and tenderness to the picture.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract, and both can produce bloody stools along with diarrhea, abdominal pain, fatigue, and weight loss. Ulcerative colitis is more consistently linked to bloody diarrhea because the inflammation targets the inner lining of the colon and rectum, where bleeding is visible and direct. Crohn’s disease can affect any part of the digestive tract from mouth to anus, and the diarrhea may or may not contain blood depending on where the inflammation is located.
Both conditions are chronic, meaning they involve periods of flare and remission. If you’re experiencing persistent bloody diarrhea along with cramping and fatigue, especially if you’re in your 20s or 30s (when IBD most commonly appears), that pattern is worth investigating.
Stomach Ulcers and Upper GI Bleeding
Bleeding from the stomach or esophagus produces dark, tarry stools rather than bright red blood. Stomach ulcers and inflammation of the esophagus or stomach lining are common culprits. Certain pain relievers, particularly NSAIDs like ibuprofen and aspirin, can irritate the stomach lining and contribute to ulcer formation over time.
Another cause of upper GI bleeding is a Mallory-Weiss tear, a small rip at the junction of the stomach and esophagus, usually caused by forceful vomiting or retching. Varices, which are swollen blood vessels in the digestive tract caused by liver disease, can also bleed heavily. Abnormalities in the blood vessels themselves, sometimes hereditary and sometimes related to chronic kidney or heart disease, are another potential source.
Colorectal Cancer
Blood in the stool is one of the possible signs of colorectal cancer, though it’s far from the most common cause of rectal bleeding. Still, it’s the reason screening matters. The CDC recommends that most people begin colorectal cancer screening at age 45. For average-risk individuals, a colonoscopy every 10 years or a yearly stool test that detects hidden blood (called a FIT test) are standard options. Rectal bleeding that is new, persistent, or accompanied by changes in bowel habits, unexplained weight loss, or a feeling that the bowel doesn’t fully empty deserves evaluation regardless of your age.
Foods and Medications That Mimic Blood
Before assuming the worst, consider what you’ve eaten or taken recently. Beets and foods with red coloring can make stool appear reddish, closely mimicking the look of blood. On the darker end, iron supplements, Pepto-Bismol (bismuth subsalicylate), activated charcoal, black licorice, blood sausage, and even large amounts of blueberries can turn stool black. The key difference is that these impostors won’t produce the sticky, tar-like consistency or foul odor of true upper GI bleeding.
How the Source Is Found
When bleeding needs investigation, doctors have several tools depending on where they suspect the source. A colonoscopy uses a flexible tube with a camera to examine the entire colon and rectum, and it’s the most thorough way to evaluate lower GI bleeding. An upper endoscopy does the same thing from above, passing a camera down the throat to inspect the esophagus, stomach, and upper small intestine. For bleeding that’s hard to locate, capsule endoscopy involves swallowing a vitamin-sized capsule with a tiny camera inside that photographs the entire digestive tract as it passes through. Blood tests check for anemia and clotting issues, while stool tests can detect blood that isn’t visible to the naked eye.
Signs That Bleeding Is an Emergency
Most rectal bleeding is not life-threatening, but significant blood loss from the GI tract can become dangerous. Seek emergency care if rectal bleeding is accompanied by rapid or shallow breathing, dizziness or lightheadedness when standing, blurred vision, fainting, confusion, nausea, cold or clammy skin, or very low urine output. These are signs the body is losing enough blood to affect circulation, and they require immediate treatment regardless of what’s causing the bleed.