Black feces may be affected by drugs and food, such as consuming iron, bismuth, blood products, etc.; it may also be caused by digestive system diseases and blood system diseases. 1. Drugs, food causes: eating iron products, bismuth agents, such as ferrous succinate, ferrous sulfate, bismuth potassium citrate, etc. may lead to black stool; eating animal offal, blood products may also lead to black stool. 2. Digestive system diseases: commonly seen in upper gastrointestinal bleeding, such as peptic ulcer, cardia mucous membrane tear, gastritis, gastric cancer, cirrhosis, esophagogastric fundal varices rupture bleeding caused by gastrointestinal hemorrhage, which can lead to black stools, and there may also be vomiting blood. 3. Other diseases: such as leukemia, hemophilia, thrombocytopenic purpura and other hematologic diseases, systemic lupus erythematosus, vasculitis, coagulation abnormalities, etc. may also lead to gastrointestinal bleeding, black stool. If the feces black in the exclusion of physiological causes, you should consult a doctor in time, under the guidance of the doctor for treatment, to avoid delaying the condition.