Black Vomit Causes In most of the cases, black vomit signals bleeding in the upper gastrointestinal (GI) tract. This bleeding could result from some underlying health conditions or illnesses, such as tumor in the lining of the esophagus (both malignant and benign), tumor in the stomach (benign and malignant), kidney disease, a tear in the blood vessels of the esophagus resulting from vomiting for a long time, yellow fever, any internal trauma to the organs and structures in the gastrointestinal tract, stomach cbd oil benefits inflammation, pancreatic cancer, acute liver failure, cirrhosis, ruptured ulcer, Duodenitis, and Portal hypertension. The reason why the vomit changes color to black is that when the upper gastrointestinal tract bleeds, the blood passes to the stomach. The enzymes that are present in the stomach break the blood and cause its color to change to black.