What Causes Stool To Be Black?

Black stool can be alarming, but it is not always a medical emergency. The color change usually comes from something you ate, a medication you took, or bleeding in your upper digestive tract. The most important step is figuring out which category applies to you. If the black color is sticky, smells foul, and looks like tar, that points to bleeding and requires prompt medical attention.

What Causes Stool To Be Black?

Black stool has two main causes: swallowed blood or ingested substances that darken the stool. Blood that has traveled through the digestive tract turns black because digestive enzymes break down the hemoglobin in red blood cells. This process creates a substance called hematin, which is dark and tarry.

Foods, supplements, and medications can also turn stool black without any bleeding. Iron supplements are a common culprit. Bismuth subsalicylate, the active ingredient in Pepto-Bismol, can turn stool black or sometimes dark green. Certain dark-colored foods like black licorice, blueberries, and blood sausage can produce the same effect.

How Can You Tell If Black Stool Is From Bleeding?

The texture and smell offer strong clues. Bleeding in the stomach or upper intestine produces stool that is sticky, black, and tar-like with a distinct foul odor. Doctors call this melena. Food-related black stool usually looks more normal in consistency and does not have that characteristic smell.

Another clue is the amount. A small amount of dark food rarely turns an entire bowel movement black. If the whole stool is black and tarry, bleeding is more likely. If you see only dark specks or streaks, food is the more probable explanation.

If you are unsure, stop eating the suspected food or supplement and watch what happens next. Stool color should return to normal within a day or two. If it stays black, seek medical advice.

What Medications and Supplements Can Cause Black Stool?

Iron supplements are the most common supplement cause. They darken stool consistently in most people who take them. This is harmless, though it can be surprising if you were not warned.

Bismuth subsalicylate, found in Pepto-Bismol and Kaopectate, also darkens stool. The bismuth combines with sulfur in the digestive tract to form bismuth sulfide, which is black. This effect is temporary and resolves once you stop taking the medication.

Activated charcoal, sometimes used for gas relief or emergency poisoning treatment, turns stool black as well. It passes through the digestive system without being absorbed, carrying the black color with it.

Some prescription medications can cause digestive bleeding that leads to black stool. Nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen can irritate the stomach lining and cause ulcers. Blood thinners such as warfarin or apixaban increase bleeding risk. If you take these medications and develop black stool, contact your doctor.

Which Foods Can Turn Stool Black?

Several foods contain pigments that survive digestion and darken stool. Black licorice is the most commonly cited example. It contains a compound that colors stool dark, and eating a significant amount can produce black bowel movements.

• Black licorice
• Blueberries
• Dark chocolate
• Blood sausage or other blood-containing foods
• Foods made with black food coloring

Blueberries contain anthocyanins, pigments that can darken stool when eaten in large quantities. The effect is more common in children who eat many blueberries at once. Dark chocolate and cookies with black food coloring can do the same.

If you ate any of these foods in the past day or two, that is likely the explanation. The color change should pass within one to two bowel movements.

When Should Black Stool Be Considered a Medical Emergency?

Black, tarry stool from bleeding requires urgent evaluation. The bleeding could come from a stomach ulcer, gastritis, esophageal varices, or a tear in the esophagus. These conditions can worsen quickly, and significant blood loss can be dangerous.

Seek emergency care if black stool is accompanied by any of these symptoms:

• Dizziness or lightheadedness
• Shortness of breath
• Rapid heart rate
• Chest pain
• Severe abdominal pain
• Vomiting blood or material that looks like coffee grounds
• Fainting

These symptoms suggest significant blood loss. Do not wait to see if they improve. Call emergency services or go to the nearest emergency department.

Even without these symptoms, black stool that persists for more than a couple of days without an obvious food or medication cause warrants a doctor’s visit. The doctor can test a stool sample for hidden blood and determine whether an endoscopy is needed.

What Other Colors of Stool Should You Watch For?

Stool color provides useful information about digestive health. Red stool usually means bleeding in the lower digestive tract, such as the colon or rectum. This could come from hemorrhoids, anal fissures, or more serious conditions like colorectal polyps or cancer.

Pale, clay-colored, or white stool suggests a problem with bile flow. Bile gives stool its normal brown color. If bile cannot reach the intestines due to a blocked bile duct, stool loses its color. This can indicate gallbladder, liver, or pancreatic issues and requires medical evaluation.

Yellow or greasy stool can indicate fat malabsorption, which may occur with conditions like celiac disease or pancreatic insufficiency. Green stool is usually harmless and often results from eating green vegetables or food passing through the digestive tract too quickly.

Any persistent change in stool color that you cannot explain should be discussed with a doctor. A single unusual stool is rarely concerning. A pattern of change over several days deserves attention.

How Is Bleeding-Related Black Stool Diagnosed?

When a doctor suspects upper digestive bleeding, they typically start with a stool test to confirm the presence of blood. A physical exam and blood tests may follow to check for anemia or signs of blood loss.

The most common diagnostic procedure is an upper endoscopy. A thin, flexible tube with a camera is passed through the mouth into the stomach and upper intestine. This allows the doctor to see the source of the bleeding directly and often treat it at the same time.

Common findings include peptic ulcers, gastritis, or tears in the esophagus. In some cases, the bleeding comes from abnormal blood vessels that can be cauterized or clipped during the procedure. The specific treatment depends entirely on what the doctor finds.

Some research suggests that upper gastrointestinal bleeding accounts for a significant portion of emergency gastroenterology admissions. Prompt diagnosis and treatment generally lead to good outcomes, but delaying care increases the risk of complications.