Blood in your stool can come from anywhere along your digestive tract, from your esophagus all the way down to your anus. The most common causes are hemorrhoids and anal fissures, but the list of possibilities ranges from completely benign to serious conditions like colorectal cancer. What the blood looks like, and where it appears, tells you a lot about where the bleeding is coming from.
What the Color of Blood Tells You
The color and appearance of blood in or on your stool is one of the most useful clues to its source. Bright red blood typically means the bleeding is in your lower colon, rectum, or anus. Dark red or maroon blood suggests the source is higher up in the colon or small intestine. Black, tarry stool often points to bleeding in the stomach, because blood changes color as it’s digested on its way through the GI tract.
You might notice blood on the toilet paper, dripping into the bowl, mixed into the stool itself, or only visible on a screening test. Each pattern points in a slightly different direction, but none of them alone can confirm a diagnosis.
Hemorrhoids and Anal Fissures
These two conditions are by far the most common reasons people see bright red blood after a bowel movement. Hemorrhoids are swollen veins in the lower rectum and anus. Most don’t cause pain, but they can bleed noticeably, especially during straining. You may also notice itching or small lumps around the anus.
Anal fissures are small tears in the lining of the anus. They’re more painful than hemorrhoids, often causing a sharp or burning sensation during and after a bowel movement. You’ll typically see blood on the toilet paper or on the surface of the stool. Fissures commonly develop from passing hard or large stools, and they usually heal on their own within a few weeks if stool consistency improves.
Diverticular Bleeding
Diverticular disease becomes increasingly common after age 40. Small pouches called diverticula form in the colon wall, and occasionally a small artery near one of these pouches erodes and bleeds directly into the colon. The hallmark of diverticular bleeding is painless rectal bleeding that can be surprisingly heavy. It often stops on its own, but because the volume of blood can be significant, it sometimes requires medical evaluation or intervention.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both cause chronic inflammation in the digestive tract, and both can produce blood in the stool. Ulcerative colitis involves inflammation in the colon, typically most severe in the rectum. Because of that location, people with ulcerative colitis tend to see visible rectal bleeding, feel urgency to use the bathroom, and pass looser stools.
Crohn’s disease can affect any part of the digestive tract, so bleeding isn’t always visible. If the inflammation is higher up and doesn’t reach the lower colon, you may have other symptoms like abdominal pain, weight loss, or diarrhea without obvious blood. Both conditions involve periods of flare-ups and remission, and bloody diarrhea paired with fever, severe abdominal pain, or weight loss warrants prompt medical attention.
Peptic Ulcers and Upper GI Bleeding
Open sores on the stomach lining or the upper part of the small intestine can bleed slowly or rapidly. Because the blood travels the full length of the digestive tract, it’s broken down along the way and turns stool black and tarry rather than red. This type of stool has a distinct, unusually foul smell.
Tears in the esophagus, known as Mallory-Weiss tears, and enlarged veins in the esophagus called varices can also cause significant upper GI bleeding. These conditions are less common than ulcers but can produce heavy blood loss. If your stool is consistently black and sticky, that’s worth investigating promptly.
Colorectal Cancer and Polyps
This is the possibility most people worry about when they search for causes of blood in stool, and it’s worth taking seriously without panicking. Colorectal cancer can cause bleeding that’s visible or so subtle it only shows up on a screening test. Other signs include a persistent change in bowel habits, unexplained weight loss, and a feeling that your bowel doesn’t fully empty.
The risk rises substantially with age. Colorectal cancer rates per 100,000 people jump from about 9 in adults under 50 to roughly 70 in those aged 50 to 64, and 157 in people 65 and older. The U.S. Preventive Services Task Force recommends screening starting at age 45 for average-risk adults, with options including a yearly stool test (called FIT) or a colonoscopy every 10 years. FIT is more sensitive and specific than older stool blood tests, and it’s a simple at-home option. Polyps, which are precancerous growths in the colon, can also bleed and are typically removed during a colonoscopy before they ever become cancerous.
Foods and Medications That Mimic Blood
Not everything that looks like blood in your stool actually is blood. Beets, red gelatin, tomato-based foods, and certain food dyes can turn stool red. Iron supplements can make stool appear black and tarry in a way that closely resembles upper GI bleeding. Bismuth-based products like Pepto-Bismol have the same effect.
Some substances also interfere with stool tests used to detect hidden blood. Aspirin, ibuprofen, vitamin C supplements, and even rare red meat can cause false results on certain screening tests. If you’re preparing for a stool blood test, your doctor may ask you to avoid these for a few days beforehand.
Signs That Need Immediate Attention
Most rectal bleeding is minor and stops on its own, but certain combinations of symptoms signal a more urgent problem. Heavy or continuous bleeding, especially if accompanied by severe abdominal pain or cramping, warrants a trip to the emergency room.
Significant blood loss can lead to shock. Warning signs include rapid or shallow breathing, dizziness or lightheadedness when standing, blurred vision, confusion, fainting, cold or clammy skin, and reduced urine output. These symptoms alongside rectal bleeding call for emergency medical help immediately. Even without dramatic bleeding, blood in your stool that persists for more than a few days, or that you can’t clearly attribute to something like a known hemorrhoid, is worth getting evaluated.