Drinking milk may cause diarrhea symptoms because patients with lactose intolerance, after drinking milk, will cause diarrhea symptoms to manifest. Because of the lack of lactase in the body of patients with this condition, milk entering the digestive tract can only be excreted in the form of metabolites because it cannot be broken down into galactose and glucose, which can be absorbed and used by the body. Therefore, it causes patients to have symptoms such as diarrhea and thin stools. In addition, patients with chronic gastroenteritis, ulcerative ileitis, Helicobacter pylori infection and other conditions can also induce pathological diarrhea after drinking milk. This is because the local tissues of the digestive tract can be seriously affected by organic lesions, which can affect its normal functioning. Milk protein is a substance that is more difficult to be decomposed and absorbed by the gastrointestinal tissues, so patients who consume it may also experience such adverse symptomatic reactions due to the increased functional burden.