What Causes Black Stools?
Stool color is typically yellow or dark yellow. In daily life, some individuals may pass black stool. Black stool (melena) often results from multiple factors—for example, consumption of blood-based foods (e.g., pig blood) or iron-rich foods; use of iron supplements; or gastrointestinal bleeding caused by digestive tract disorders. So, what causes black stool? Below, we address this question.
What Causes Black Stool?
1. Pathological Factors
Malignant tumors such as rectal cancer or colon cancer may also cause melena. Hematologic disorders can similarly lead to black stool. Moreover, gastrointestinal diseases—including gastric ulcers, gastritis, and intestinal polyps—may cause bleeding. Iron in the blood reacts with intestinal bacteria to form ferrous sulfide, a primary contributor to black stool. Therefore, black stool warrants prompt medical evaluation to rule out these serious conditions.
2. Dietary Factors
Black stool may also result from recent intake of foods rich in natural pigments—such as pork liver, spinach, or pig blood—which can darken stool. In such cases, patients need not be alarmed; adjusting dietary habits and limiting intake of these foods usually prevents recurrence. Additionally, medications—including iron supplements, certain traditional Chinese medicines, Gastrium (a gastric mucosal protectant), and colloidal bismuth pectin—can also cause black stool.
3. Chronic Constipation
Chronic constipation may also contribute to black stool. Sluggish gastrointestinal motility leads to prolonged retention of food residues in the digestive tract, delaying digestion and absorption—and potentially resulting in bowel movements only every few days. Prolonged accumulation of metabolic waste and toxins may further darken stool color. To alleviate this, patients are advised to consume more fiber-rich, laxative-promoting foods; if necessary, pharmacologic interventions may be considered.
The above outlines common causes of black stool. We hope this information is helpful to you.
