Why is the stool black?

The phenomenon of black stool may be related to diet, drugs, diseases and other factors, such as: 1. The patient eats too much iron-rich food such as animal liver, animal blood, bayberry, mulberry, etc., which reacts with sulfide in intestinal tract to form iron sulfide, so that stool appears black;2. Drug factors, such as bismuth for treating stomach diseases and iron for enriching blood;3. Upper gastrointestinal bleeding;4. Blood diseases, such as allergic purpura, etc.