Changes in stool color are common, and dark brown or black stool can be alarming. Stool color varies daily, influenced by diet and medications. Understanding the potential reasons behind these changes helps determine when they are harmless or indicate a serious issue.
Understanding Normal Stool Appearance
Healthy stool ranges in color from medium to dark brown. This brown color comes from bile, a yellowish-green fluid produced by the liver, and bilirubin, a pigment formed when red blood cells break down. As these compounds travel through the digestive tract, they undergo chemical changes due to enzymes and bacteria, turning the stool brown.
Healthy stool has a consistent, sausage-like shape and a soft to firm texture, allowing for easy passage. Variations in color or consistency that persist for more than a day or two without an obvious cause can signal a change in digestive health.
Common Dietary and Medication Influences
Dietary choices often cause temporary changes in stool color, including darkening. Consuming dark-colored foods such as black licorice, blueberries, or beets can lead to stools appearing dark brown or black. Foods containing dark food dyes or high amounts of iron, like red meat or blood sausage, may also contribute to this effect.
Certain medications and supplements can also darken stool. Iron supplements are a common cause, as unabsorbed iron passing through the digestive tract can result in dark green or black stool. Bismuth subsalicylate, found in some over-the-counter stomach remedies, is another common cause. This compound reacts with small amounts of sulfur in the digestive system to form bismuth sulfide, a black substance that darkens the stool. This effect is temporary and resolves once the food or medication is no longer consumed.
Underlying Health Conditions
While dietary and medication influences are common, dark brown or black, tarry stool can indicate bleeding in the upper gastrointestinal (GI) tract. This type of stool, medically termed melena, results from blood being digested as it travels through the esophagus, stomach, and small intestine. Digestive chemicals interact with hemoglobin in blood, changing its color to black and giving the stool a sticky, tar-like consistency and a foul odor.
Conditions that can cause upper GI bleeding include peptic ulcers, which are sores in the lining of the stomach or duodenum. Gastritis, an inflammation of the stomach lining, can also lead to bleeding and dark stools. Esophageal varices, enlarged veins in the esophagus often linked to liver disease, can rupture and cause bleeding resulting in black, tarry stools. Less commonly, certain cancers of the esophagus, stomach, or pancreas can also cause GI bleeding, resulting in dark stools.
When to Consult a Doctor
Seek medical attention if dark brown or black stool persists without a clear dietary or medication cause. Immediate medical evaluation is warranted for specific signs. These include stool that is black and tarry, has a strong and foul odor, or is accompanied by other concerning symptoms.
Accompanying symptoms that should prompt a doctor’s visit include:
- Abdominal pain or discomfort
- Nausea
- Vomiting (especially if it contains blood or looks like coffee grounds)
- Unexplained weight loss
- Fatigue
- Dizziness
- Weakness or lightheadedness
If you experience any of these symptoms alongside dark stools, or if the change in stool color is sudden and unexplained, consulting a healthcare professional is advised to determine the cause and ensure appropriate care.