Blood exposed to gastric acids turns black and tarry (sticky). This is called melena and is a sign of an upper gastrointestinal bleed.

Is it bad if poop is black?

Black stools are a worrisome symptom because it may be due to a large amount of bleeding into the digestive system, most often from the upper GI tract including the esophagus, stomach, and duodenum. Red blood cells are broken down by digestive enzymes in the intestine and turn the stool black.

Is black poop ever normal?

Black stool may be normal in some cases and caused by ingesting certain substances or medications, such as iron supplements. However, black stool can also be caused by a serious condition, such as bleeding in the digestive tract caused by a peptic ulcer.