Drinking pure milk diarrhea may be due to lactose intolerance, poor gastrointestinal function, allergy to milk and other reasons. 1. Lactose intolerance: Pure milk contains lactose, lactose digestion and absorption of lactose requires the participation of lactase enzyme, part of the body does not contain lactase enzyme or lactase enzyme less, can not be digested lactose, so it will lead to drink pure milk diarrhea symptoms. 2. poor gastrointestinal function: some people have poor gastrointestinal function or gastrointestinal diseases, after drinking milk can not be digested and absorbed, resulting in diarrhea after drinking milk. 3. Allergy to milk: personal constitution is different, some people are allergic to milk, can lead to drink milk diarrhea, abdominal pain, vomiting symptoms, and often rashes, itchy skin and other manifestations. Drinking pure milk diarrhea should go to the hospital to identify the cause, and standardized treatment under the guidance of the doctor.