Drinking pure milk will have diarrhea, mainly considering lactose intolerance, pure milk is cooler, patients with allergic reactions and so on. 1. Lactose intolerance: patients with low levels of lactase, lactose intolerance, when eating a lot of pure milk, will lead to diarrhea. 2. Pure milk is too cold: when pure milk is just taken out of the refrigerator, the milk is too cold, and by drinking a lot of cold food, it will stimulate the gastrointestinal tract and accelerate gastrointestinal peristalsis, which will lead to diarrhea. 3. Allergy: when the patient is allergic to pure milk, but also because of the antigen-antibody reaction, gastrointestinal peristalsis, causing diarrhea, abdominal pain, dizziness, skin rash and other adverse reactions. In addition, drinking pure milk diarrhea, there may be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment and treatment.