What Does Blood in Your Stool Look Like?

Blood in your stool can look dramatically different depending on where the bleeding originates and how much time the blood spends traveling through your digestive tract. It ranges from bright red streaks on toilet paper to jet-black, tarry bowel movements, and sometimes it is entirely invisible to the naked eye. The color alone is a surprisingly reliable clue about the source of the problem, but many people never see blood at all and only learn about it through a screening test.

Bright Red Blood

The most recognizable form is fresh, bright red blood, known medically as hematochezia. You might notice it on the toilet paper after wiping, coating the surface of your stool, dripping into the bowl, or mixing into a loose stool. Because the blood has not had time to be broken down by digestive enzymes, it retains its red color, which almost always means the bleeding source is in the lower part of the digestive tract: the colon, rectum, or anus.

Research using standardized color cards found that when patients identified their stool as the brightest red shade on the card, it pointed to a colorectal or anorectal source with a positive predictive value of 1.00, meaning every patient who chose that color turned out to have lower gastrointestinal bleeding.¹ In most cases, the culprit is something relatively benign. Hemorrhoids are the single most common cause of bright red rectal bleeding in adults, and the blood is arteriolar in origin, which is why it can look alarmingly vivid even when the underlying problem is not dangerous.² Anal fissures, which are small tears in the lining of the anus, produce a similar bright red appearance and are another frequent cause.³

That said, bright red blood is not always harmless. Ulcerative colitis, a form of inflammatory bowel disease that affects the colon and rectum, commonly presents with bloody diarrhea. Blood in the stool, along with fecal urgency and mucus, is one of the hallmark symptoms that distinguishes ulcerative colitis from Crohn’s disease, where visible bleeding is less frequent.⁴ Colorectal polyps and tumors in the lower colon can also shed red blood. In young adults under 40 with bloody stool, risk factors for finding a cancerous or precancerous polyp include a family history of colorectal cancer, higher body mass index, and diabetes.⁵

Black, Tarry Stools

When bleeding occurs higher in the digestive tract, in the stomach or the first part of the small intestine, the blood is exposed to stomach acid and digestive enzymes for hours before it exits. That chemical exposure oxidizes the hemoglobin and turns the blood dark. The result is a stool that is black, sticky, and has a distinct, unusually foul smell. This is called melena, and it looks nothing like the bright red blood most people picture when they think of blood in their stool.

The tarry consistency is a key feature. Plenty of things can make a stool dark, but true melena has an almost shiny, tar-like quality. In the same color-card study mentioned above, patients who pointed to the blackest shade on the card were almost certainly bleeding from an upper gastrointestinal source. The positive predictive value of that black color for upper GI bleeding was 0.95 when patients self-selected the color, and 0.98 when matched directly against the stool sample.¹

The most common cause of melena is peptic ulcer disease, particularly ulcers in the duodenum, the section of the small intestine just beyond the stomach. These ulcers are frequently linked to an infection with the bacterium H. pylori or to long-term use of NSAIDs like ibuprofen and aspirin.⁶ Gastritis, esophagitis, and esophageal varices (swollen veins in the esophagus, often tied to liver disease) are other upper GI sources that can produce black tarry stool.

One important distinction: iron supplements and bismuth subsalicylate (the active ingredient in Pepto-Bismol) also turn stool black. But these produce a more uniformly dark, sometimes greenish-black color without the characteristic tarry stickiness or the unmistakable odor. If you are taking either of those and notice dark stool, do not assume it is medication-related without considering other symptoms. True melena warrants prompt medical attention because upper GI bleeding can become serious quickly.

Maroon Stool and the Middle Ground

Not all bloody stool falls neatly into “bright red” or “black.” A maroon or burgundy color suggests bleeding from somewhere in between, often the small bowel or the right side of the colon. The blood has had some transit time but not enough to turn fully black. A case report of neonatal volvulus described stool that was “a maroon color which suggests a small bowel source, with a currant jelly consistency, a mixture of blood, mucosal sloughing and mucus.”⁷ While that case involved a surgical emergency in a newborn, maroon-colored stool in adults can appear with a range of small bowel conditions, diverticular bleeding, or rapid upper GI bleeding where transit is fast enough that the blood does not fully darken.

Maroon stool is less common than either frank red blood or classic melena, and it tends to be more diagnostically challenging. Clinicians sometimes categorize it separately because the bleeding source is harder to pin down with a standard upper endoscopy or colonoscopy, and further testing of the small bowel may be needed.⁸

Blood You Cannot See

Perhaps the most medically significant form of blood in the stool is the kind you never notice. Occult gastrointestinal bleeding, meaning blood present in amounts too small to change the color of your stool or to be visible on toilet paper, often presents with no symptoms at all. You may only learn about it through a positive fecal occult blood test or when a doctor investigates unexplained iron-deficiency anemia.⁸

Occult blood testing was originally developed as a screening tool for colorectal cancer, but a positive result does not automatically mean cancer. Causes range from colon polyps and early-stage tumors to inflammatory conditions, and even intestinal parasitic infections can trigger a positive test.⁹ The test is designed to catch bleeding you would never know about otherwise, which is precisely why it is part of routine colorectal cancer screening programs.

Two main types of home stool tests exist for detecting occult blood. The older guaiac-based tests (gFOBT) rely on a chemical reaction with the heme portion of hemoglobin, while the newer fecal immunochemical tests (FIT) use antibodies that specifically detect human hemoglobin. FIT consistently outperforms gFOBT. A Cochrane review found that gFOBT detected about 15% of advanced neoplasms, while FIT caught roughly a quarter to a third, depending on the threshold used.¹⁰ In a head-to-head comparison of specific test brands, the best-performing FIT detected advanced colorectal neoplasia with about two to three times the sensitivity of the best gFOBT, while maintaining similarly high specificity.¹¹ If your doctor offers you a choice, FIT is the better screening option. Neither test replaces a colonoscopy when one is indicated, but they are a practical first-pass tool for catching hidden bleeding.

Foods and Substances That Fake It

Before you panic about a red or dark toilet bowl, consider what you have eaten in the past day or two. Beets are one of the most notorious culprits. The deep purple-red pigment in beets can survive digestion and produce a stool color that looks shockingly like blood, sometimes staining the entire toilet bowl. A physician writing in JAMA decades ago described encountering several cases each August of “late-summer pseudomelena,” noting that patients arrived “thoroughly alarmed” by what they assumed was a bloody bowel movement.¹² The same pigment can turn urine pink, which is called beeturia and is harmless.

Other foods and supplements that can change stool color include:

Iron supplements: dark green to black stools, sometimes mistaken for melena
Bismuth medications: black stools from Pepto-Bismol or similar products
Red food dyes: brightly colored drinks, gelatin, or candies can tint stool red or pink
Leafy greens: large amounts of spinach or kale can produce very dark green stool
Blueberries and dark cherries: can darken stool substantially

The practical test is straightforward: if you recently ate something in the list above and the color change resolves within a day or two, food is the likely explanation. But if the unusual color persists, comes with pain or other symptoms, or you cannot trace it to a dietary cause, treat it as potentially real bleeding.

How Medications Affect the Picture

Several common medications can cause genuine gastrointestinal bleeding or interfere with stool-based screening tests. NSAIDs like ibuprofen, naproxen, and aspirin can irritate the stomach lining and cause small amounts of bleeding, sometimes enough to show up on a fecal occult blood test without producing any visible change in stool color. Blood thinners like warfarin and antiplatelet drugs like clopidogrel can make existing sources of bleeding worse.

This creates a practical problem for screening. A study examining fecal occult blood test results in patients on these medications found that the positive predictive value of the test for advanced colon neoplasia dropped substantially in medicated groups compared to controls. In patients not on any of these drugs, about 30% of positive tests correctly pointed to an advanced polyp or cancer, but that figure fell to roughly 20% for those on aspirin or NSAIDs and dropped to about 7% for clopidogrel users.¹³ In other words, these drugs cause more false positives, making it harder to tell whether a positive test reflects a worrisome growth or just drug-related mucosal irritation. If you are on blood thinners or daily aspirin, talk with your doctor about whether a colonoscopy makes more sense than a stool-based test for your screening.

When Visible Blood in Stool Is Actually a Good Sign

This sounds counterintuitive, but there is evidence that visible blood in the stool, when it leads to a cancer diagnosis, is associated with a better outcome than cancers found without bleeding symptoms. A study of colon cancer patients found that tumors in people who presented with visible blood in their stool were more likely to be lower grade, have features associated with better immune response, and show less vessel invasion. Patients whose cancer was flagged by visible rectal bleeding had roughly half the mortality risk compared to those whose cancer presented in other ways.¹⁴

The reason is probably that tumors causing visible bleeding tend to be in the left side of the colon or rectum, closer to the exit, where they produce noticeable symptoms earlier. Right-sided colon cancers are more likely to cause occult bleeding and iron-deficiency anemia instead, and by the time they are diagnosed, they may be more advanced. This does not mean visible bleeding is “good” in any absolute sense. It means that ignoring visible blood because you assume it is hemorrhoids can cost you the very advantage that early, obvious symptoms provide: the chance to catch something serious while it is still treatable.

Inflammatory Bowel Disease and Chronic Bloody Stool

For people with ulcerative colitis, bloody stool is not an occasional alarm but a recurring symptom that tracks with disease activity. Peranal bleeding, along with diarrhea and abdominal pain, is considered a hallmark clinical feature of ulcerative colitis.¹⁵ The blood typically appears mixed into loose or watery stool and is often accompanied by mucus, which gives the stool a slimy appearance that is distinct from the clean red blood seen with hemorrhoids. Crohn’s disease can also cause bloody stool, but it is less consistently present and depends on where in the gastrointestinal tract the inflammation is located.⁴

If you are experiencing bloody diarrhea that persists for more than a couple of weeks, especially alongside cramping, urgency, or unintentional weight loss, inflammatory bowel disease should be on the list of possibilities. These symptoms overlap with infectious colitis, so your doctor will likely want stool cultures and possibly a colonoscopy to sort things out.

Obscure Bleeding and the Small Bowel

Sometimes gastrointestinal bleeding recurs but standard evaluations come up empty. An upper endoscopy examines the esophagus, stomach, and duodenum. A colonoscopy covers the entire colon and the very end of the small intestine. Between those two scopes lies about 20 feet of small bowel that neither procedure can reach. Bleeding from this middle zone is classified as obscure gastrointestinal bleeding, and it can present as occult blood, intermittent melena, or the maroon-colored stool described earlier.⁸

Causes of small bowel bleeding include vascular malformations (abnormal clusters of small blood vessels), small bowel tumors, Crohn’s disease affecting the ileum, and NSAID-induced ulcers. Diagnosing these often requires specialized tools like video capsule endoscopy, where you swallow a pill-sized camera that photographs the entire small intestine as it passes through, or device-assisted enteroscopy, where a flexible scope is advanced deep into the small bowel. These are not first-line tests, but they become important when standard workups fail to explain recurrent bleeding.

A Quick Visual Guide

Because the appearance of bloody stool varies so much, here is a practical breakdown of what you might see and what it tends to mean:

Bright red on paper or surface of stool: usually anorectal, most commonly hemorrhoids or a fissure
Red blood mixed into stool: colonic source such as a polyp, diverticular disease, or colitis
Maroon or burgundy stool: small bowel bleeding or rapid upper GI bleed
Black, tarry, sticky stool with foul odor: upper GI source like a stomach or duodenal ulcer
Black but not tarry: possibly iron supplements or bismuth, not necessarily bleeding
Normal-looking stool with positive test: occult bleeding, needs further evaluation

These are patterns, not rules. A brisk upper GI bleed can produce red blood if the transit is fast enough, and a slow lower GI bleed can occasionally darken to maroon. Context matters: your other symptoms, your medication list, your diet in the past 48 hours, and your medical history all factor into what the color actually means. The one guideline that applies universally is that new, unexplained blood in your stool deserves a conversation with a doctor, even when the most likely explanation is something benign.

1
PubMed. An objective measure of stool color for differentiating upper from lower gastrointestinal bleeding
2
PubMed Central. What are hemorrhoids and what is their relationship to the portal venous system?
3
PubMed Central. Benign anorectal disease: hemorrhoids, fissures, and fistulas
4
Arquivos de Gastroenterologia. The onset of clinical manifestations in inflammatory bowel disease patients
5
PubMed. Identification of risk factors for neoplastic colonic polyps in young adults with bloody stool in comparison with those without symptom
6
PubMed Central. Causes of Melena and Effective Examination Strategies in Children
7
Elsevier / Journal of Pediatric Surgery Case Reports. Acute neonatal volvulus with congenital enteric duplication, presenting with “currant jelly” stool
8
PubMed Central. Diagnosis of gastrointestinal bleeding: A practical guide for clinicians
9
PubMed Central. Fecal Occult Blood Test and Gastrointestinal Parasitic Infection
10
PubMed Central. Guaiac‐based faecal occult blood tests versus faecal immunochemical tests for colorectal cancer screening in average‐risk individuals
11
PubMed. Superior diagnostic performance of faecal immunochemical tests for haemoglobin in a head-to-head comparison with guaiac based faecal occult blood test among 2235 participants of screening colonoscopy
12
JAMA. Discoloration of Stools From Beets
13
PubMed. Fecal occult blood test in patients on low-dose aspirin, warfarin, clopidogrel, or non-steroidal anti-inflammatory drugs
14
PubMed. Colon cancer: association of histopathological parameters and patients’ survival with clinical presentation
15
PubMed Central. Inflammatory Bowel Disease