Is a Little Blood in Stool Normal? Know When to Act

A small amount of blood in your stool is common, but it is never truly “normal” in the sense that you should expect or ignore it. Population surveys suggest that roughly one in five adults notices blood in their stool within any given year, yet fewer than a third of them visit a doctor about it.¹ Most of the time the cause is something minor like hemorrhoids or a small tear in the anal lining, but the same symptom can also be an early sign of colorectal cancer, inflammatory bowel disease, or other conditions that benefit enormously from early treatment. Understanding what to watch for and when to act can save you unnecessary worry on one hand, and a dangerous delay on the other.

How Common Is Rectal Bleeding?

Rectal bleeding is far more widespread than most people assume. In a UK postal survey, about a quarter of respondents reported noticing blood in their stool at some point, and the majority of recent bleeders had seen it within the past year.² A separate population-based study found that about 18% of adults reported blood in their stool in the previous twelve months alone.¹ Despite those high numbers, most people never bring it up with a doctor. Only about four in ten people who notice rectal bleeding ever seek medical advice for it.²

The main thing that separated those who did see a doctor from those who didn’t was perception of seriousness. People who thought their bleeding might mean something worrying were far more likely to seek help, while those who assumed it was “just hemorrhoids” tended to wait it out.² That gap matters, because while most rectal bleeding does come from benign causes, a small but meaningful fraction does not. Among patients over age 34 who consulted a doctor about rectal bleeding, about 3.4% turned out to have colorectal cancer.³ That number is low enough to be reassuring in most individual cases, but high enough that dismissing the symptom entirely is a gamble.

The Most Common Harmless Causes

Hemorrhoids are the leading cause of bright red blood on toilet paper or in the bowl after a bowel movement. These swollen blood vessels around the anus or lower rectum can bleed with minimal provocation, especially during straining. Internal hemorrhoids are particularly prone to painless bleeding, which is why you might see blood without any discomfort at all. External hemorrhoids tend to cause more pain and itching, but both types can produce blood that looks alarming despite being medically minor.

Anal fissures are the second most frequent culprit, especially in younger adults. A fissure is a small tear in the skin lining the anal canal, often triggered by passing a hard or large stool. The bleeding is typically bright red and accompanied by a sharp, burning pain during and after a bowel movement that can last well over an hour.⁴ Fissures usually heal on their own within a few weeks if stool is kept soft, though chronic fissures sometimes need treatment.

Beyond hemorrhoids and fissures, benign polyps in the colon can bleed intermittently. Most polyps are harmless, though some types carry a risk of eventually becoming cancerous, which is one reason screening colonoscopies aim to find and remove them. Rectal prolapse, where tissue slips out of the anus, can also cause minor bleeding and mucus discharge.

What the Color and Appearance Tell You

Not all bloody stool looks the same, and the differences give useful clues about where the bleeding is coming from. Gastrointestinal bleeding presents in several distinct forms: bright red blood on the surface of stool or on toilet paper (hematochezia), dark tarry stools with a distinctive foul smell (melena), or blood that is invisible to the naked eye and only detected by a lab test (occult blood).⁵

Bright red blood usually means the source is close to the exit: the rectum, anus, or lower colon. This is the type most often linked to hemorrhoids, fissures, or low-lying polyps. Maroon or dark red blood mixed into the stool tends to come from higher in the colon or even the small intestine. Black, tarry stool is a sign that blood has been digested on its way through the gut, pointing to a source in the stomach or upper intestine, such as an ulcer. If your stool looks black and sticky, that warrants prompt medical attention even if you feel fine otherwise.

One common source of confusion: certain foods and supplements can mimic bloody stool. Beets, red gelatin, and tomato-based foods can tint stool red, while iron supplements and bismuth (the active ingredient in some antacids) can turn stool black. If you’ve recently eaten one of these and the color change is a one-time event, the cause is likely dietary rather than medical. But if you aren’t sure, it is always better to check.

When Bleeding Points to Something More Serious

The critical question isn’t whether you see blood, it’s what pattern the bleeding follows and what other symptoms come along with it. Blood that appears once after a particularly hard bowel movement and then stops is far less worrying than blood that shows up repeatedly over days or weeks, especially if the amount is increasing.

In one study of patients referred for investigation of rectal bleeding, colorectal cancer was diagnosed in 15 patients and polyps in 11.⁶ Cancer-related bleeding tends to be persistent rather than occasional, and it is more likely to be mixed into the stool rather than just coating the surface or appearing on the paper. That said, cancer can also produce bright red blood that looks just like a hemorrhoid bleed, which is why appearance alone isn’t a reliable way to rule it out.

You should contact a doctor relatively promptly if you notice any of the following alongside blood in your stool:

Change in bowel habits: new constipation or diarrhea lasting more than a few weeks, or stools that become noticeably thinner.
Unintentional weight loss: dropping weight without trying, especially if accompanied by fatigue.
Blood mixed into the stool: as opposed to blood on the surface, which is more typical of hemorrhoids.
Dark or tarry stools: suggesting a bleed higher in the digestive tract.
Heavy or worsening bleeding: enough to discolor the toilet water or soak through a pad.
Abdominal pain or cramping: persistent discomfort rather than the brief pain associated with a fissure.
Age over 45 without recent screening: colorectal cancer risk rises with age, and screening guidelines now recommend starting at 45 for average-risk adults.

A sudden large volume of painless rectal bleeding in an older adult can indicate diverticular bleeding. Diverticulosis, where small pouches form in the colon wall, is extremely common after age 60, but fewer than 5% of people with diverticulosis ever experience bleeding from it. When it does happen, it tends to come on abruptly and heavily.⁷ Most episodes stop on their own, but the volume of blood can be large enough to require emergency evaluation.

Blood Thinners and Medications

If you take blood-thinning medications, rectal bleeding takes on a different dimension. Anticoagulants and antiplatelet drugs don’t cause bleeding by themselves, but they can amplify bleeding from an existing source (a hemorrhoid, a polyp, a fissure) that might otherwise have been too minor to notice. In a study of elderly patients presenting with rectal bleeding, the medications involved spanned several common categories: direct oral anticoagulants were taken by about 35% of patients, aspirin by roughly a third, clopidogrel by about 15%, and warfarin by about 14%.⁸

The tricky part for both patients and doctors is deciding what to do about the medication. Stopping a blood thinner carries its own risks, including stroke or heart attack in people who take these drugs for cardiovascular protection. In practice, many patients are restarted on their medications after the acute episode resolves: about 60% of aspirin users in the study were recommenced on the drug, and roughly 62% of warfarin users resumed treatment.⁸ The point here isn’t to scare you off your medication, but to flag that you should mention it to your doctor any time you notice rectal bleeding. These decisions need to be made on a case-by-case basis, and you should never stop or change a blood thinner on your own because you saw some blood.

Infections That Can Cause Bloody Stool

Food poisoning and gut infections are a common but often overlooked cause of bloody stool. Bacterial pathogens like Salmonella, E. coli, Shigella, and Campylobacter can all inflame the intestinal lining enough to cause bleeding. In a study of stool samples from patients with foodborne illness, abdominal pain and diarrhea were the most common presenting symptoms, occurring in 80% and 75% of cases respectively, and the most frequently isolated bacteria were E. coli and Salmonella species.⁹

Infection-related bloody stool almost always comes with other obvious symptoms: diarrhea, cramping, nausea, and sometimes fever. The onset is typically sudden, often traceable to a suspect meal or an outbreak situation. The bleeding in these cases usually resolves once the infection clears, whether on its own or with antibiotics if a bacterial cause is confirmed. If bloody diarrhea lasts more than a couple of days, involves high fever, or occurs in a very young child, an elderly person, or someone with a weakened immune system, medical evaluation shouldn’t wait.

Exercise-Induced Bleeding

Endurance athletes sometimes discover blood in their stool during or after intense training, and it catches many of them off guard. Gastrointestinal symptoms are actually quite common among distance runners and other endurance athletes, with reported rates ranging from 20% to 86% depending on the sport and intensity.¹⁰ These symptoms range from nausea and cramps to outright gastrointestinal bleeding.

The mechanism behind this is straightforward: during sustained, high-intensity exercise, your body redirects blood flow away from the digestive organs and toward your working muscles and skin. The intestines, temporarily starved of their normal blood supply, can develop small areas of reduced oxygen that damage the gut lining. Most exercise-induced GI bleeding shows up as occult blood, meaning you wouldn’t see it without a test, but occasionally it can be visible.¹⁰ The bleeding is usually self-limiting and resolves with rest. If you’re a runner or cyclist who regularly notices blood after long efforts, mention it to your doctor. In rare cases, exercise-induced ischemic colitis can be severe enough to need treatment, and it’s worth establishing that nothing else is going on.

Blood in a Baby’s Diaper

Finding blood in an infant’s stool is understandably terrifying for new parents, but the causes in babies are different from those in adults. In a review of neonates (newborns) presenting with bloody stools, the single most common cause was cow’s milk protein allergy, accounting for more than half of cases. Swallowed maternal blood (from cracked nipples during breastfeeding) was the second most common explanation, followed by viral enteritis and, more rarely, necrotizing enterocolitis in very ill premature infants. Anal fissures accounted for about 5% of cases.¹¹

Cow’s milk protein allergy is worth knowing about because it can occur even in exclusively breastfed babies if the mother is consuming dairy. The blood is usually just small streaks or flecks in an otherwise normal-looking stool. Switching the mother’s diet (or switching to a specialized formula) typically resolves the issue within a couple of weeks. Swallowed blood looks more alarming than it is: the baby is fine, and the blood simply passed through the digestive tract without causing harm.

Any bloody stool in an infant should still be evaluated by a pediatrician, particularly if the baby seems irritable, refuses to feed, has a distended abdomen, or appears unwell. In older children and toddlers, the causes start to look more like those in adults, with constipation-related fissures and infections topping the list.

How Doctors Figure Out the Source

If you report rectal bleeding to your doctor, the investigation usually starts simple and gets more involved only if the situation calls for it. A physical exam, including a digital rectal exam, can identify hemorrhoids, fissures, and masses close to the anal opening. Your doctor may also order a fecal immunochemical test, or FIT, which detects tiny amounts of human blood in stool that aren’t visible to the eye.

FIT has largely replaced the older guaiac-based stool test for screening purposes because it is more sensitive at picking up colorectal cancer and precancerous growths.¹² That said, FIT’s ability to catch cancer depends partly on the cancer’s size and stage. Early-stage tumors are detected with a sensitivity around 68%, while more advanced tumors are caught about 90% of the time.¹³ This means FIT is a solid screening tool, but a negative result doesn’t guarantee nothing is there, especially for small or early-stage growths. If symptoms persist or red flags are present, your doctor may recommend a colonoscopy regardless of the FIT result.

Colonoscopy remains the gold standard for evaluating rectal bleeding when there is concern about cancer, inflammatory bowel disease, or other significant pathology. In a study of patients referred through a fast-track pathway with rectal bleeding and a positive FIT, colonoscopy found significant bowel disease in about a quarter of cases, including cancer in 18% of those with significant findings, inflammatory bowel disease in about 24%, and large polyps in the rest.¹⁴ Flexible sigmoidoscopy, which examines only the lower portion of the colon, is sometimes used as a less invasive alternative, particularly in younger patients whose bleeding pattern suggests a low-lying source. It won’t catch problems higher up in the colon, but for straightforward cases in younger adults it can be a reasonable first step.¹⁵

Why So Many People Avoid Getting Checked

Given how common rectal bleeding is, the low rate of medical consultation is striking. Some of the reasons are practical, including limited access, time constraints, and cost. But research consistently points to emotional barriers as the bigger obstacle. In a cross-sectional study of people with hemorrhoidal symptoms, the most commonly reported barriers to seeking medical care were embarrassment and fear of invasive diagnostic procedures. Colonoscopy and digital rectal exams were each identified as major deterrents by roughly 39% of respondents.¹⁶

This avoidance has real consequences. Colorectal cancer caught early, before it has spread beyond the bowel wall, has a survival rate above 90%. Caught late, after it has spread to distant organs, the survival rate drops dramatically. The difference between those two scenarios can come down to whether someone brought up a few weeks of rectal bleeding at a routine visit or shrugged it off as hemorrhoids. Doctors see rectal symptoms constantly and will not be fazed by your description. The brief awkwardness of a conversation or exam is trivially small compared to what’s at stake.

People who perceive their bleeding as potentially serious are much more likely to seek help, which suggests that better public awareness of what rectal bleeding can mean would close part of this gap.² If you’re reading this article because you noticed blood and you’re uncertain, that uncertainty alone is reason enough to bring it up at your next appointment, or to make one sooner.

Occult Bleeding and Hidden Blood Loss

Some of the most consequential gastrointestinal bleeding is the kind you can’t see at all. Occult bleeding, where blood is present in the stool but not visible, can continue for weeks or months without obvious symptoms. The first sign is often unexplained fatigue, dizziness, or a blood test that comes back showing iron deficiency anemia.⁵ If your doctor finds you’re anemic and can’t explain it with diet or other obvious causes, they’ll often order a stool test and possibly endoscopic evaluation to look for a slow-bleeding source in the stomach, small intestine, or colon.

Obscure bleeding takes this a step further. This is the clinical term for recurrent GI bleeding where both an upper endoscopy and colonoscopy have come back clean, meaning the source is typically in the small intestine, a stretch of bowel that’s harder to examine with standard tools.⁵ Capsule endoscopy, where you swallow a tiny camera that photographs the gut as it passes through, has become the usual next step for tracking down these elusive sources. Finding the cause sometimes takes patience and multiple tests, but chronic hidden blood loss can lead to significant health problems if it goes unaddressed.