Drinking pure milk diarrhea can be caused by allergies, lactose intolerance or chronic intestinal diseases. 1. Allergy: pure milk protein content is relatively high, if there is an allergy, it may lead to intestinal mucosal edema, and the phenomenon of drinking pure milk on the diarrhea. 2. Lactose intolerance: when the body lacks the enzyme lactase to digest lactose, lactose intolerance symptoms such as diarrhea, bloating, and abdominal pain may occur when drinking pure milk and other dairy products. 3. gastrointestinal diseases: if you have enteritis, gastritis and other chronic gastrointestinal diseases, gastrointestinal digestive function is relatively poor, in taking pure milk and other protein-rich foods, may lead to indigestion, gastrointestinal peristalsis accelerated and the appearance of a drink of pure milk on the phenomenon of diarrhea. There may also be other causes of diarrhea when drinking milk, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.