In general, black streaks in the stool may be caused by eating blood products, mulberries and other foods, but also peptic ulcer and other diseases caused by upper gastrointestinal bleeding, which produces black stool. 1. Food factors: daily dietary intake of food rich in pigment, such as sheep blood, duck blood, mulberry, and other foods, which pigment is not fully metabolized by the body, resulting in black streaks in the stool. 2. Upper gastrointestinal bleeding: (1) peptic ulcer: including gastric ulcer and duodenal ulcer. Due to factors such as Helicobacter pylori and viruses, the mucosa of the digestive tract is congested and edematous, or even eroded, on which mechanical friction of food or corrosion of gastric acid may cause bleeding of the ulcer surface, producing symptoms such as black stools. (2) Cirrhosis: Cirrhosis may cause portal hypertension, which may further cause rupture and bleeding of the esophageal venous plexus at the base of the stomach, resulting in vomiting blood and black stools. (3) Acute erosive hemorrhagic gastritis: after the gastric mucosa is eroded by alcohol, non-steroidal anti-inflammatory drugs such as celecoxib, etc., causing acute inflammation of the gastric mucosa, with oedema, congestion, erosion and hemorrhage, which will result in black stools and other phenomena. The black stripes in the stool may also be caused by gastrointestinal tumors, and it is recommended to consult a doctor in time for a clear diagnosis and targeted treatment.