2. Gastrointestinal Bleeding
Black stool may also occur due to gastrointestinal bleeding. When the blood passes through the digestive tract, it gets digested and turns black. The bleeding may occur anywhere in the digestive tract, such as the esophagus, stomach, or small intestine. Bleeding in the upper digestive tract is more likely to cause black stool, while bleeding in the lower digestive tract may cause red or maroon-colored stool.