Some people experience diarrhea after drinking milk, which is called lactose intolerance. The main carbohydrate in milk is lactose, and after drinking milk, lactose needs to be absorbed by lactase in the small intestine, but some people are congenitally deficient in lactase, so lactose cannot be broken down and absorbed, and the lactose then enters the large intestine, making the water in the large intestine not fully absorbed by the body. After drinking a certain amount of milk or eating other foods containing lactose, patients with lactose intolerance usually have diarrhea symptoms between half an hour and several hours similar to those after using laxatives, mostly watery stools, the severity of which is related to the amount of lactose consumed, and in severe cases, nausea, abdominal distension, and even vomiting and diarrhea. For breastfeeding infants and children, there is also diaper rash and growth retardation. Therefore, if you are determined to be lactose intolerant, you should avoid consuming excessive amounts of milk or dairy products containing lactose.