Lactose is an important nutrient in mammalian milk, and lactose in breast milk and milk powder is the most important source of energy for infants and young children. After entering the human body, lactose is broken down into glucose and galactose by the action of small intestine lactase, and the hydrolyzed galactose is a component of the glycolipids of brain and neural tissue. Lactase deficiency or reduced activity can lead to lactose malabsorption, and undigested lactose entering the colon can be fermented by bacteria to produce short-chain fatty acids such as acetic acid and propionic acid and gases such as carbon dioxide, which in turn increases intestinal osmotic pressure, resulting in clinical manifestations such as intestinal tinnitus, abdominal pain, bloating and osmotic diarrhea, called lactose intolerance. People who are prone to lactose intolerance are 1. infants with diarrhea for more than 1 week; 2. infants with frequent infantile intestinal cramps; 3. infants with frequent bloating; 4. premature infants who eat milk well but have poor nutrition and loose stools also have lactose intolerance; 5. adults who have diarrhea after drinking milk are lactose intolerant; 5. diarrhea after intestinal surgery, a large proportion of which are lactose intolerant. Taking lactase orally before each milk intake can supplement your own lactase deficiency and relieve diarrhea, bloating and abdominal pain caused by lactose intolerance. Lactase should be taken with water at about 37 degrees Celsius. If you are taking milk powder, you can mix lactase with milk powder and take it together. Lactase can be effective 3-5 days after taking lactase, depending on the length of time the baby’s symptoms appear, the application of lactase usually takes 10-15 days to control the symptoms.