Black tarry stools are usually caused by upper gastrointestinal bleeding, which is a relatively serious pathological change, and prompt medical attention is recommended. Under normal circumstances, the stool is soft and formed, yellowish-brown, if there is bleeding in the digestive tract, the hemoglobin in the blood and gastric acid formed by the acidification of n-ferric hemoglobin, which combines with sulfur compounds in the intestinal tract to form ferrous sulfide, resulting in a black stool color and shiny like tar. Generally, when the daily bleeding volume of the body is more than 50~75ml, the stool can be tar-like. There are many diseases that cause upper gastrointestinal bleeding, among which the more common diseases are peptic ulcer, acute gastric mucosal lesions and other gastrointestinal diseases and allergic purpura, systemic lupus erythematosus and other systemic diseases. In addition, drugs, environment, bad habits, can also trigger upper gastrointestinal bleeding, resulting in black tarry stools. If you have black tarry stools, it is recommended that you go to a regular hospital in time to find out the cause and actively treat it.