When drinking milk, there are physiological reasons such as milk spoilage, lactose intolerance and pathological reasons such as gastritis and gastric ulcer. 1. Physiological reasons: If you drink expired and spoiled milk, bacterial infection is likely to occur, causing acute gastritis, resulting in stomach pain. In addition, some people have lactose intolerance, and milk contains a lot of lactose, in this case, drinking milk will appear stomach pain, and may be accompanied by diarrhea and other symptoms. 2. Pathological reasons: gastric diseases, such as gastric ulcer, gastritis and other diseases, the gastric mucosa is more fragile, the stomach’s digestive and absorptive function is poor, after drinking milk is not easy to digest and absorb, but also aggravate the condition of the gastric ulcer or gastritis, causing stomach pain, abdominal distension and other manifestations. Drinking milk stomach pain, there may be other reasons, should 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 or treatment.