Normal people eating foods containing iron such as animal blood, pig liver and kelp can form black iron sulfide in human intestines, and can also make feces black, while taking bismuth, charcoal powder and some traditional Chinese medicines can also make feces discolored. If this is the case, it is a normal phenomenon, so don't panic.

Therefore, when it is found that the stool turns black, we must distinguish it carefully, so that we can neither see the wind nor the rain, nor be careless. Black stool caused by bleeding generally has a history of primary disease (such as stomach pain, ulcer, liver cirrhosis, etc.) and symptoms of corresponding diseases. The appearance of black stool is black and shiny, and with the increase of bleeding volume, the body may have symptoms of blood loss such as dizziness, weakness, thirst, palpitation, accelerated heart rate, pale face and even fainting. The "fake black stool" often has a special eating history, that is, it occurs after taking drugs that can cause black stool or eating animal blood products. The color of black stool is relatively dark, and it rarely shines except eating animal blood. Moreover, after stopping taking such foods (drugs), the "black stool" disappears within three days, and it will not be accompanied by any other discomfort symptoms.

Green is watery or mushy, with sour smell and foam, which is more common in diseases such as indigestion and intestinal dysfunction. If the green stool is mixed with pus, it is the manifestation of acute enteritis or bacillary dysentery. After major abdominal surgery or patients receiving extensive antibiotic treatment, such as sudden appearance of green watery stool with fishy smell and gray-white flaky translucent egg-green pseudomembrane, it may be Staphylococcus aureus enteritis. In addition, eating a lot of food containing chlorophyll, or the acidity in the intestine is too high, will also make the feces turn green.

However, if it is a long-term black stool with constipation, it is recommended to go to the hospital for examination, early detection and early treatment.

When the esophagus, stomach, duodenum, upper jejunum, pancreas and biliary tract bleed, the iron of hemoglobin in red blood cells combines with sulfide to form iron sulfide under the action of intestinal bacteria, thus making the feces appear black. This black stool is black and shiny, and its appearance is like tar, so it is also called tarry stool. Tarry stool is a manifestation of upper gastrointestinal bleeding.