There are several reasons for black stools: 1, if there is frequent constipation, the intestinal tract of fecal residue, fecal lumps due to the absorption of a large amount of water, which can lead to color changes and the appearance of black stools. 2, if you eat black-colored food, such as pig’s blood, sheep’s blood, or drugs such as ferrous sulfate, bismuth citrate are prone to the situation of black stools, especially if you eat bismuth citrate 3, that is, upper gastrointestinal bleeding, most of them are due to gastric ulcer, duodenal bulb ulcer, cardia mucosa tear, or upper gastrointestinal bleeding due to esophagitis, etc. If the blood stays in the intestine for a long time, trivalent iron ions will become divalent iron ions resulting in black stool, it is best to If the blood stays in the intestine for a long time, the trivalent iron ions will turn into divalent iron ions and lead to black stool.