Tarry stool, known medically as melena, is strikingly dark, often jet-black, with a sticky, tar-like consistency and a distinctly foul smell that sets it apart from ordinary dark-colored bowel movements. Its appearance signals that blood has been digested as it traveled through the gastrointestinal tract, and it almost always points to bleeding somewhere in the upper digestive system. The look alone is hard to mistake once you have seen it, but understanding what produces it and what to do about it matters far more than recognizing the color.
What Tarry Stool Actually Looks Like
Melena is the passage of black, tarry stools, distinct from hematochezia, which is the passage of fresh red blood in or with stool.1PubMed. Hematemesis, Melena, and Hematochezia The color ranges from coal-black to a very dark maroon, and the texture is characteristically sticky or gooey rather than firm. If you were to smear it on a surface, it would leave a dark, adherent streak. The smell is another distinguishing feature: most people describe it as uniquely offensive, sharper and more metallic than ordinary stool odor. That smell comes from partially digested blood, specifically from the breakdown of hemoglobin by stomach acid and intestinal bacteria into compounds called hematin and other sulfur-containing byproducts.
The reason the color is black rather than red is transit time. When blood enters the upper digestive tract and spends several hours moving through the stomach and small intestine, acid and enzymes chemically alter it. By the time it reaches the colon and exits the body, the iron in hemoglobin has been oxidized, turning it dark. Fresh red blood in the stool, by contrast, usually indicates bleeding from a source much lower in the digestive tract, such as the colon or rectum, where there is not enough transit time for the blood to be chemically changed.
Common Causes of Upper Gastrointestinal Bleeding
Since tarry stool is a sign of digested blood, the underlying question is always: where is the bleeding coming from? The answer is almost always somewhere above the lower part of the small intestine. Several conditions account for the vast majority of cases.
Peptic Ulcers
Open sores in the lining of the stomach or the first part of the small intestine (the duodenum) are among the most frequent culprits. These ulcers erode into blood vessels in the gut wall, releasing blood into the digestive tract. In one pediatric study reviewing causes of melena in children, duodenal ulcers were the single most common finding on endoscopy, followed by esophageal conditions and gastric ulcers.2PubMed Central. Causes of Melena and Effective Examination Strategies in Children In adults, the pattern is similar: peptic ulcers remain the leading cause of upper gastrointestinal bleeding worldwide, driven largely by infection with the bacterium Helicobacter pylori and the widespread use of nonsteroidal anti-inflammatory drugs like ibuprofen, aspirin, and naproxen.
Esophageal and Gastric Varices
In people with liver disease, especially cirrhosis, increased pressure in the veins that drain the digestive organs can cause those veins to swell and balloon, particularly in the esophagus and stomach. These swollen vessels, called varices, have thin walls and can rupture, sometimes producing massive bleeding. A case report of a 50-year-old man with liver cirrhosis describes classic presentation: he arrived with bloody vomiting and black tarry stool, along with other signs of advanced liver disease such as fluid buildup in the abdomen and visible collateral veins on the skin.3The Indonesian Journal of Gastroenterology, Hepatology, and Digestive Endoscopy. COVID-19 in A Liver Cirrhosis Patient Variceal bleeding tends to be heavy and is considered a medical emergency. It was the second most common cause of melena identified in the pediatric endoscopy study as well.2PubMed Central. Causes of Melena and Effective Examination Strategies in Children
Mucosal Tears at the Junction of the Esophagus and Stomach
Forceful or prolonged vomiting, retching, or coughing can physically tear the lining where the esophagus meets the stomach. This is known as a Mallory-Weiss tear. A classic study of 11 patients with these tears found that eight of them presented with gastrointestinal bleeding, though the textbook history of vomiting before the bleeding appeared in fewer than half the cases.4PubMed Central. Mucosal tears at the oesophagogastric junction (the Mallory-Weiss syndrome) That last point is worth noting: many people assume a Mallory-Weiss tear always follows a dramatic episode of vomiting, but it can occur without a clear preceding event, making it easy to overlook.
Stomach and Upper GI Cancers
Tumors in the stomach or upper intestine can ulcerate or invade blood vessels, causing chronic or acute bleeding. Black tarry stool is considered an important alarm symptom in the context of gastric cancer and often accompanies anemia in advanced or ulcerated tumors.5Binaytara. 5 Early Signs and Symptoms of Stomach Cancer You Shouldn’t Ignore Melena from malignancy is not always dramatic; sometimes the bleeding is slow and intermittent, producing stools that are only slightly darker than normal and easy to dismiss. Persistent unexplained dark stools, especially combined with unintentional weight loss, loss of appetite, or worsening anemia, warrant prompt investigation.
When Dark Stool Is Not Melena
Not every dark or black bowel movement is tarry stool. Several common substances can turn stool very dark without any bleeding at all, and this is one of the most frequent sources of unnecessary alarm. Iron supplements are a classic example: they routinely produce dark green to black stools that can look alarming but have a normal consistency and lack the sticky, tar-like texture and distinctive foul odor of melena. Bismuth subsalicylate, the active ingredient in some over-the-counter stomach medications, does the same thing. Certain foods can also darken stool, including black licorice, blueberries, and beets (though beets more commonly cause a reddish discoloration).
The key differences are texture and smell. Stool darkened by iron or bismuth tends to be normally formed and does not have the uniquely offensive metallic odor. True melena is loose to semi-formed, viscously sticky, and the smell is hard to ignore. If you are uncertain, a doctor can run a simple test called a fecal occult blood test on a stool sample, which detects hidden blood regardless of color. This is particularly useful when someone is taking iron supplements and cannot tell whether new darkening of stool is the supplement or something more concerning.
Warning Signs That Demand Emergency Care
Tarry stool on its own is a reason to see a doctor, but certain accompanying symptoms escalate the situation to an emergency. You should seek immediate care if black tarry stool occurs alongside dizziness, weakness, fainting, vomiting blood, a rapid heartbeat, or severe abdominal pain.6Ubie Doctor’s Note. Black and Tarry Stool: Causes, Symptoms, and When It’s an Emergency These signs suggest significant blood loss and possible hemodynamic instability, meaning the body is struggling to maintain adequate blood pressure and circulation.
Even without those dramatic symptoms, tarry stool that persists over more than one or two bowel movements should not be brushed off. Slow, chronic bleeding can gradually deplete your red blood cells, leading to anemia that creeps up so gradually you adapt to feeling tired and short of breath and assume it is normal. A basic blood count at the doctor’s office can catch this.
How Doctors Figure Out Where the Bleeding Is Coming From
Once a doctor suspects upper gastrointestinal bleeding based on the appearance of the stool (or on vomiting blood), the investigation follows a fairly predictable path. The goal is to locate the bleeding source, assess its severity, and stop the bleeding if it is still active.
Blood Tests and the BUN-to-Creatinine Ratio
One of the first clues comes from routine blood work. When blood is digested in the gut, the proteins in it are absorbed and broken down into urea, which shows up as an elevated blood urea nitrogen (BUN) level on a basic metabolic panel. This does not happen when bleeding is from the lower digestive tract, because blood from the colon exits too quickly to be digested and absorbed. The ratio of BUN to creatinine in the blood can help distinguish upper from lower gastrointestinal bleeding. A systematic review and meta-analysis found that this ratio demonstrates moderate accuracy for making the distinction, performing best at a threshold of roughly 22 or above, and may help with early clinical triage, especially when the presentation is not obviously pointing in one direction.7PubMed. Blood Urea Nitrogen-to-Creatinine Ratio to Differentiate Upper From Lower Gastrointestinal Bleeding: A Systematic Review and Meta-Analysis One study found that a cutoff around 23 had both high sensitivity and high specificity for identifying upper GI bleeding.8PubMed Central. The role of BUN/creatinine ratio in determining the severity of gastrointestinal bleeding and bleeding localization Other studies have been more conservative in their estimates, with one reporting lower sensitivity at a higher cutoff of 35.9PubMed Central. Blood Urea Nitrogen to Creatinine ratio in Differentiation of Upper and Lower Gastrointestinal Bleedings; a Diagnostic Accuracy Study The takeaway for the reader is that this blood test is useful but not definitive on its own; it gives doctors one more piece of the puzzle while they arrange more direct investigation.
Endoscopy
The gold standard for finding and treating the source of upper GI bleeding is an upper endoscopy, where a thin flexible camera is passed through the mouth into the esophagus, stomach, and upper small intestine. The doctor can visually inspect the lining, identify ulcers, tears, varices, or tumors, and in many cases treat the bleeding on the spot using clips, cauterization, or injection of medications that constrict blood vessels. In the pediatric melena study, endoscopy identified a specific cause in the large majority of cases, with duodenal ulcers, esophageal varices, esophagitis, and gastric ulcers accounting for most findings, and some patients underwent endoscopic treatment during the same procedure.2PubMed Central. Causes of Melena and Effective Examination Strategies in Children Timing matters: guidelines generally recommend performing endoscopy within 24 hours of presentation for acute upper GI bleeding, and even sooner if there are signs of significant ongoing blood loss.
Risk Scoring and Clinical Triage
Not every person who arrives at the hospital with melena needs aggressive intervention. Some episodes resolve on their own, while others require blood transfusions, endoscopic treatment, or even surgery. Doctors use standardized risk scores to help sort patients into lower-risk and higher-risk categories. A review of these scoring systems found that the Glasgow Blatchford Score, which uses simple clinical and laboratory data like hemoglobin level, blood pressure, heart rate, and the presence of melena or blood vomiting, performs best at identifying very low-risk patients who are unlikely to need hospital-based treatment or to die from the bleed.10PubMed Central. A Review of Risk Scores within Upper Gastrointestinal Bleeding For patients who score at the very low end, the evidence supports safe outpatient management rather than hospital admission, which matters a great deal for avoiding unnecessary hospital stays and their associated costs and risks.
For patients who score higher, the score helps prioritize how quickly endoscopy is performed and whether intensive care monitoring is warranted. The practical value of these scores is that they push back against both extremes of clinical instinct: the temptation to admit everyone “just in case” and the temptation to reassure too quickly when the numbers suggest a sicker patient than they appear.
Tarry Stool in Newborns and Young Children
Melena in newborns presents a unique diagnostic puzzle. In the first few days of life, dark stools are normal: meconium, the newborn’s first stool, is thick, sticky, and greenish-black, and it can easily be confused with melena. True bloody stools in a newborn, however, raise the question of whether the blood belongs to the baby or to the mother. Infants can swallow maternal blood during delivery or while breastfeeding from cracked nipples. A classic laboratory test was developed specifically to answer this question by exploiting the fact that fetal hemoglobin is more resistant to chemical breakdown than adult hemoglobin. When the bloody stool is mixed with an alkali solution, adult hemoglobin changes color while fetal hemoglobin stays pink, quickly telling clinicians whether the blood is the mother’s or the baby’s.11The Journal of Pediatrics. “Melena” neonatorum: The swallowed blood syndrome: A simple test for the differentiation of adult and fetal hemoglobin in bloody stools If the blood turns out to be maternal, the situation is generally benign and requires no treatment for the infant. If it is the baby’s own blood, further investigation into causes like vitamin K deficiency bleeding, necrotizing enterocolitis, or anatomical abnormalities becomes necessary.
In older children, the causes of melena largely mirror those in adults, though the relative frequency differs. As noted earlier, peptic ulcers and esophageal varices are the top findings on endoscopy in pediatric patients with melena, but inflammatory conditions of the esophagus and stomach also feature prominently.2PubMed Central. Causes of Melena and Effective Examination Strategies in Children Because children are less likely to describe their symptoms precisely, caregivers should watch for stool color changes, pallor, fatigue, or unexplained irritability as indirect clues.
Medications and Lifestyle Factors That Increase Risk
Several widely used medications raise the risk of upper gastrointestinal bleeding and, by extension, the risk of developing tarry stool. Nonsteroidal anti-inflammatory drugs are the most well-known offenders. Aspirin, ibuprofen, and naproxen all interfere with the protective lining of the stomach and can promote ulcer formation, especially with long-term or high-dose use. Blood-thinning medications like warfarin and the newer direct oral anticoagulants do not cause ulcers themselves but make any existing bleeding source bleed more freely and for longer, turning what might have been a minor ooze into a clinically significant bleed.
Alcohol is another major contributor. Chronic heavy drinking damages the stomach lining directly and, over time, can lead to liver disease and the portal hypertension that causes esophageal varices. Smoking also increases the risk of peptic ulcers by impairing the stomach’s ability to repair its own lining and by increasing acid production. Stress alone does not typically cause bleeding ulcers in otherwise healthy people, despite the popular belief, but physiological stress from severe illness, major surgery, or critical care can produce what are called stress ulcers in hospitalized patients.
If you take daily aspirin or another anti-inflammatory for a chronic condition, ask your doctor whether you also need a proton pump inhibitor or similar acid-reducing medication to protect your stomach lining. This is standard preventive practice for people on long-term NSAID therapy who have additional risk factors such as age over 65, a history of ulcers, or concurrent use of blood thinners.
How Long Tarry Stool Persists After Bleeding Stops
One fact that catches many people off guard is that tarry stools can continue for several days after the bleeding source has been treated or has stopped on its own. Blood that was already in the digestive tract before treatment still has to make its way through the remaining length of the intestines, and transit through the colon can take anywhere from 12 hours to a few days depending on the individual. So seeing one or two more dark stools after a hospital procedure does not necessarily mean the bleeding has restarted. Doctors typically watch for a return to normal stool color over two to three days and monitor hemoglobin levels to confirm that the patient is not continuing to lose blood.
If tarry stools persist beyond three to five days after treatment, or if they return after a period of normal-colored stools, that raises concern for rebleeding and usually prompts another round of investigation. Rebleeding rates vary by cause: peptic ulcers treated endoscopically rebleed in a meaningful minority of cases, and variceal bleeding has a particularly high rebleeding rate without ongoing medical therapy to reduce portal pressure. Knowing this helps set realistic expectations during recovery rather than panicking at every dark bowel movement or, conversely, ignoring a genuine recurrence.