Lactose intolerance is a non-infectious diarrhea caused by low secretion of lactase and inability to completely digest and break down the lactose in breast milk or cow’s milk, also known as lactase deficiency. In China, it can occur in infancy, childhood and adulthood. Generally, the diagnosis can be clarified according to its clinical manifestations and clinical auxiliary examinations. 1. Judged by clinical manifestations Symptoms may include abdominal pain, bloating, diarrhea, gas production and vomiting, which usually start to occur between half an hour and two hours after drinking milk, and the severity depends on the amount the patient eats or drinks. If there are no corresponding symptoms once lactose is eliminated from the diet, the diagnosis can be tentatively confirmed. 2. Judgment based on auxiliary tests (1) Hydrogen breath test: 12 hours before the test, the patient must fast and then ingest 25g of lactose. If the patient has a high level of hydrogen or methane in the breath, it indicates a high chance of lactose intolerance. This is the most accurate method of testing for lactose intolerance. However, because this test may cause severe diarrhea and requires a relatively long fast, it is not usually used on infants and young children; (2) Other tests: stool acidity and alkalinity, stool reducing sugar, urinary galactose, and intestinal pathology sections can also be used to diagnose lactose intolerance. For patients with lactose intolerance, treatment can be carried out in the following two ways: 1. General treatment: if the number of stools does not increase significantly and does not affect growth and development, temporary observation can be made; in mild cases, the intake of breast milk or formula can be reduced, and in severe lactose intolerance, lactose-containing dairy products should be avoided and milk substitutes and lactose-free dairy products can be chosen. The number of breastfeeding can be gradually increased according to the child’s tolerance; 2. Medication: appropriate administration of lactase, which facilitates the digestion and absorption of lactose, thus alleviating the symptoms of lactose intolerance.