Black colored stool can be a normal physiological condition or can be caused by disease. Physiological conditions are mainly caused by food and medications, such as various blood products such as pig’s blood, sheep’s blood, duck’s blood, etc., and various black colored foods such as black sesame and eggplant. In addition, drugs can also cause dark stools, such as iron supplements for anemia, and bismuth supplements to protect the gastric mucosa in the treatment of stomach diseases. Pathological cases of dark stool mainly refers to bleeding in the digestive tract, mainly a small amount of bleeding in the upper gastrointestinal tract, such as gastric erosion, ulcers, or even a small amount of bleeding in the stomach caused by malignant lesions, can cause the symptoms of dark stool.