Blood in your stool is usually caused by something treatable, like hemorrhoids or a small tear in the skin around your anus. But it can also signal conditions that need medical attention, from infections to inflammatory bowel disease to, less commonly, colorectal cancer. The color of the blood, how much there is, and whether you have other symptoms all help narrow down 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, usually the colon, rectum, or anus. You might see it on the toilet paper, streaked across the surface of your stool, or dripping into the bowl. This is the most common type people notice, and it often points to issues close to the exit point.
Dark, tarry, sticky stool with a strong odor usually means bleeding higher up in the digestive tract, above the colon. Blood that travels a longer distance through your intestines gets digested along the way, turning it black. If your stool looks like this, the source is more likely your stomach or small intestine, and it generally warrants prompt medical evaluation.
Hemorrhoids and Anal Fissures
These two conditions account for the majority of bright red rectal bleeding, especially in otherwise healthy adults. They’re different problems, but both involve the tissue right around your anus.
Hemorrhoids are swollen veins around the anus. They often cause painless bleeding, which is why people are caught off guard when they see red in the toilet. You might also notice itching, mild discomfort, or small lumps near the opening. Straining during bowel movements, sitting for long periods, and pregnancy all increase the risk. Most hemorrhoids resolve on their own or with simple changes like more fiber and water.
Anal fissures are small tears in the skin of the anus. Unlike hemorrhoids, fissures almost always hurt, particularly during and right after a bowel movement. You may feel a sharp, stinging pain along with burning or itching that lingers. Fissures are more prone to bacterial infection, which can slow healing. They’re commonly caused by passing hard, large stools and tend to heal within a few weeks with stool softeners and warm baths.
Infections That Cause Bloody Stool
Certain bacterial infections inflame the lining of your intestines enough to cause bleeding. The bacteria most often responsible include E. coli, Salmonella, Campylobacter, Shigella, and C. diff. These infections typically come from contaminated food or water, and they tend to hit fast: you’ll usually have diarrhea (sometimes bloody), stomach cramps, nausea, and possibly a high fever. The combination of fever and bloody diarrhea is a hallmark of bacterial gastroenteritis and distinguishes it from a viral stomach bug, which rarely produces blood.
Most bacterial infections clear up within a week, though some require antibiotics. If you’ve recently traveled, eaten something questionable, or been on antibiotics (which can trigger C. diff), an infection is worth considering.
Diverticular Bleeding
Diverticulosis, where small pouches form in the wall of the colon, is extremely common as people age. Most people with these pouches never know they have them. But about 10% experience bleeding at some point, which happens when hard stool passing through one of the pouches stretches or erodes a blood vessel until it breaks.
The bleeding from diverticulosis is distinctive because it’s usually painless and sudden. You may pass a large amount of dark red or maroon blood with little warning. It often stops on its own, but the volume can be alarming enough to send people to the emergency room.
Inflammatory Bowel Disease
Ulcerative colitis and Crohn’s disease both involve chronic inflammation of the digestive tract, and rectal bleeding is one of their core symptoms. Ulcerative colitis, which affects the colon and rectum, causes frequent bloody diarrhea along with urgency and cramping. Crohn’s disease can affect any part of the digestive tract and may produce either bright red blood or dark, tarry stools depending on where the inflammation is.
Severe bleeding episodes in Crohn’s disease are relatively uncommon, affecting roughly 1% to 5.5% of patients over their lifetime. But for about a third of those people, heavy bleeding is actually the first sign that leads to diagnosis. IBD is a lifelong condition, but modern treatments can control symptoms and reduce flares significantly.
Colorectal Cancer
This is the possibility most people are worried about when they search this question. The reassuring news is that most rectal bleeding is not cancer. But it’s important to know the pattern: almost half of young people diagnosed with colon cancer had rectal bleeding as a symptom. Early-onset colon cancer, diagnosed before age 50, is rising. In the early 2000s, about 5% to 7% of colon cancer cases were considered early onset. That number has climbed to around 10%.
Bleeding from colorectal cancer can look identical to hemorrhoid bleeding, which is exactly why persistent or unexplained bleeding deserves investigation. Warning signs that raise concern include a change in bowel habits lasting more than a few weeks, unexplained weight loss, a feeling that your bowel doesn’t empty completely, fatigue, and bleeding that doesn’t improve with typical hemorrhoid treatment. Screening colonoscopies are now recommended starting at age 45 for average-risk adults.
Foods That Mimic Blood in Stool
Before assuming the worst, consider what you’ve eaten recently. Beets are the most common culprit. They contain pigments that can turn both stool and urine red, sometimes vividly enough to look like blood. This effect, sometimes called pseudo-hematochezia, can appear two to three days after eating beets or taking beet supplements. Red gelatin, tomato soup, red food dyes, and certain fruit punches can do the same. Bismuth-based medications (like some stomach remedies) can turn stool black, mimicking the tarry appearance of upper digestive bleeding.
If you suspect food is the cause, the color change should resolve within a day or two of stopping the food. If it doesn’t, the red isn’t from your diet.
When Rectal Bleeding Is an Emergency
Most rectal bleeding doesn’t require a trip to the emergency room, but certain situations do. Seek urgent care if you experience:
- Heavy bleeding or large blood clots in your stool
- Lightheadedness, dizziness, or feeling faint, which can signal a sudden drop in blood pressure from blood loss
- Sudden severe bleeding that starts without warning
- Consistent bleeding that continues for several days without slowing
Even if the bleeding is small and painless, it’s worth mentioning to your doctor if it recurs or lasts more than a week or two. A brief evaluation can rule out anything serious and, in most cases, confirm a straightforward cause that’s easy to manage.