When the upper gastrointestinal tract is severely diseased, iron from the hemoglobin in the red blood cells combines with sulfide to form iron sulfide under the action of intestinal bacteria, resulting in black and shiny stools with the appearance of tar, so it is also called tar-like stool. But are all “black stools” bleeding? The color of the stool and the usual diet and drugs also have a certain relationship: 1, common can cause the stool for brown or even black food: animal blood products (chicken blood, goose blood, duck blood, pig blood, sheep blood, etc.), animal offal (beef, pig liver, sheep liver, duck liver, etc.), because the iron in animal blood can also be produced in the human intestine reaction, the same formation of black iron sulfide, so that the color of the stool becomes black. In addition, if you eat more mulberry, purple, prune jam, etc., are likely to make the color of the stool black. 2, drugs: oral activated charcoal end, blood iron (ferrous sulfate, etc.), bismuth (colloidal bismuth, Lizudra, etc.) and certain Chinese medicines for the treatment of gastric diseases, can also cause the stool to become black. Therefore, if the stool suddenly turns black, first of all, you need to exclude food and drugs, usually stop using the relevant food and drugs, the stool will gradually turn yellow.