There is no such thing as “yellow stool or black stool”; normal stool is yellow, while black stool may be caused by diet, medication, or diseases such as upper gastrointestinal bleeding, as long as it is not caused by diseases, black stool is normal. Normal stools are yellow in color and have a banana-like shape. Black stool is usually seen after eating iron-rich green vegetables, animal blood and other foods, or taking iron, bismuth and other drugs, generally stop eating such foods or drugs after the color of the stool can return to normal, so the above situations are normal phenomena. In the case of upper gastrointestinal bleeding, the blood enters the intestines and is digested and absorbed in the intestines, and the iron in the hemoglobin changes from trivalent iron to divalent iron, which leads to black stools, which can also cause black stools. It is recommended to go to the hospital in time to see a doctor and take active treatment after eliminating factors such as diet and medication that affect the color of the stool.