Blood in your stool is surprisingly common. Roughly one in seven otherwise healthy adults report it at some point, and the cause is usually something treatable like hemorrhoids or a small tear in the anal lining. That said, the color, amount, and accompanying symptoms all matter, because they point to very different parts of your digestive tract and very different conditions.
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 originates in the lower digestive tract, meaning the colon, rectum, or anus. It looks red because it hasn’t traveled far or been exposed to digestive enzymes. Dark, tarry, almost black stool points to bleeding higher up, in the stomach or esophagus. Blood that makes that longer journey gets broken down along the way, turning the stool dark and sticky.
Bright red blood on toilet paper, on the surface of your stool, or dripping into the bowl usually signals a problem near the exit: hemorrhoids, a fissure, or inflammation in the colon. Black, tarry stool is more closely associated with stomach ulcers or inflammation of the esophagus or stomach lining. If you’re seeing maroon-colored stool, the source is often somewhere in between.
Hemorrhoids: The Most Common Culprit
Internal hemorrhoids are the reason most people notice blood after a bowel movement. They sit inside the rectum where you can’t see or feel them, and they rarely hurt. What they do is bleed, usually small amounts of bright red blood you’ll spot on the toilet paper or in the bowl. Straining during a bowel movement, sitting on the toilet too long, or passing hard stool irritates them enough to cause this painless bleeding. Sometimes an internal hemorrhoid pushes through the anal opening (a prolapsed hemorrhoid), which can cause more discomfort.
External hemorrhoids, by contrast, tend to cause itching and pain more than bleeding, though they can bleed if a blood clot forms inside them. Most hemorrhoid bleeding resolves on its own with more fiber, more water, and less time straining on the toilet. Persistent or recurring bleeding still deserves a medical evaluation to rule out other causes.
Anal Fissures
A fissure is a small tear in the lining of the anus. It typically happens from passing a large or hard stool, chronic diarrhea, or any activity that stretches the anal tissue beyond its limit. The lining of the anus is thin and tears relatively easily. Unlike hemorrhoids, fissures tend to cause a sharp, stinging pain during and after bowel movements alongside the bright red blood. Most acute fissures heal within a few weeks with stool softeners and warm baths, but chronic fissures that last longer than six to eight weeks sometimes need further treatment.
Diverticular Bleeding
Diverticulosis, the formation of small pouches in the colon wall, is actually the most common cause of significant lower digestive bleeding in adults. These pouches develop at weak points where blood vessels penetrate the muscle layer. Factors like regular use of anti-inflammatory pain relievers (ibuprofen, aspirin), blood thinners, smoking, and alcohol increase the risk of these pouches bleeding.
The bleeding from diverticulosis can be dramatic. It often starts suddenly, is painless, and produces a large volume of bright red or maroon blood. In many cases it stops on its own, but the volume alone can be alarming enough to send someone to the emergency room, and that’s the right call. Heavy, sudden rectal bleeding always warrants urgent evaluation.
Inflammatory Bowel Disease
Two chronic conditions fall under the umbrella of inflammatory bowel disease: ulcerative colitis and Crohn’s disease. Both can cause blood in the stool, but they do it differently.
Ulcerative colitis starts at the rectum and stays in the colon, inflaming only the innermost lining. Because the inflammation sits so close to the exit, bloody diarrhea is one of its hallmark symptoms, often accompanied by lower abdominal cramps and urgency. Crohn’s disease, on the other hand, can affect any part of the digestive tract and penetrates deeper layers of the intestinal wall. It more commonly causes nonbloody diarrhea and abdominal pain, though it can lead to bleeding indirectly through complications like fissures, fistulas (abnormal tunnels between tissues), or abscesses around the anus.
If you’re experiencing ongoing bloody diarrhea, cramping, and weight loss, particularly if you’re in your 20s or 30s (when these conditions often first appear), bring it up with your doctor promptly. Both conditions are manageable but require proper diagnosis.
Infections That Cause Bloody Stool
Certain bacterial infections can inflame the intestinal lining enough to cause bloody diarrhea. The bacteria most commonly responsible include E. coli, Salmonella, Campylobacter, Shigella, and C. diff. These infections usually come from contaminated food or water, though C. diff often follows a course of antibiotics that disrupts normal gut bacteria.
High fever paired with bloody diarrhea is a strong signal that the cause is bacterial rather than viral. Most bacterial gastroenteritis resolves within a week, but significant dehydration or persistent bloody stool may require medical treatment.
Stomach Ulcers and Upper Digestive Bleeding
When bleeding originates in the stomach or esophagus, it typically shows up as black, tarry stool rather than visible red blood. Stomach ulcers and esophageal inflammation are the most common causes. Another possibility is a Mallory-Weiss tear, a small rip at the junction of the stomach and esophagus usually caused by prolonged vomiting or retching.
Problems with blood vessels themselves can also cause upper or lower digestive bleeding. These vascular issues may be hereditary or related to chronic kidney or heart disease, and certain medications, particularly anti-inflammatory pain relievers, can make them worse.
Colorectal Cancer: Rare but Important
This is likely the concern behind your search, and it’s worth putting into perspective. Most rectal bleeding is not cancer. But colorectal cancer can cause blood in the stool, often in amounts too small to see with the naked eye. When visible, the blood may be dark or mixed into the stool rather than sitting on top of it.
The CDC recommends that most adults begin screening for colorectal cancer at age 45. For average-risk people, a colonoscopy every 10 years is the standard interval. If you’re between 45 and 75 and haven’t been screened, new or unexplained blood in your stool is a reasonable reason to schedule that first screening. If you’re under 45, your doctor will weigh other symptoms and risk factors (family history, unexplained weight loss, changes in bowel habits lasting weeks) to decide whether earlier evaluation makes sense.
Stool-based screening tests can detect hidden blood you can’t see. The newer version, called FIT, picks up about 76% of colorectal cancers, compared to about 39% for the older type of stool test. Neither is perfect, which is why colonoscopy remains the gold standard for a thorough look, but FIT is a practical first step for routine screening.
Symptoms That Need Immediate Attention
Most rectal bleeding can wait for a scheduled doctor’s appointment. But certain combinations of symptoms signal a medical emergency. Call 911 or get to an emergency room if you experience heavy or continuous rectal bleeding along with any of the following:
- Rapid, shallow breathing
- Dizziness or lightheadedness when you stand up
- Fainting or confusion
- Cold, clammy, or pale skin
- Blurred vision
- Very low urine output
These are signs of shock from significant blood loss. Rectal bleeding with severe abdominal pain or cramping also warrants an emergency visit, even if the bleeding itself doesn’t seem heavy. For everything else, a nonemergency appointment with your doctor is the right next step. Even when the cause turns out to be hemorrhoids, confirming that with a professional is worth the visit.