Normal stool is yellow in color with a foul odor. There are many reasons for black and smelly stools, such as food factors, constipation, drug effects, gastrointestinal bleeding, blood system diseases, etc. You need to consult a gastroenterologist to clarify the specific causes and provide targeted treatment. 1, food factors: eating iron-containing foods, such as pig blood, duck blood, pork, pig liver, etc., will cause a chemical reaction with the human intestinal tract, forming iron sulfide, resulting in black, smelly stools. This is a normal phenomenon, no need to deal with; 2, constipation: the stool stays in the body for too long, then there will be smelly, black stool. Constipation should be actively treated, the less severe symptoms can be regulated by diet, such as eating fiber-rich corn, celery, etc., you can also drink yogurt, honey water to promote intestinal peristalsis and relieve constipation. Those with more serious symptoms can use simple laxatives, such as lactulose, under the guidance of a doctor; 3, the impact of drugs: such as iron supplements for blood, activated charcoal, bismuth for the treatment of stomach diseases and certain Chinese medicines, etc., may also lead to black stools after taking. If, in addition to black stool, odor, no other symptoms, no treatment is required. If accompanied by other symptoms, such as constipation, the drug can be suspended; 4, gastrointestinal bleeding: peptic ulcer, chronic gastritis, cirrhosis combined with ruptured esophagogastric fundic varices, gastric cancer, gastric mucosal lesions and other causes of upper gastrointestinal bleeding, due to bleeding iron in the red blood cells in the hemoglobin under the action of intestinal bacteria, combined with sulfide to form iron sulfide, thus making the stool appear black and smelly. Should promptly go to the hospital for stool occult blood test or imaging, clear cause after symptomatic treatment; 5, blood system diseases: such as hemophilia, leukemia, etc., lesions involving the digestive tract may lead to black smelly stool, need to go to the hospital for related examinations, and actively treat the original disease.