Lactase is a biological enzyme in human body, which mainly decomposes lactose and hydrolyzes lactose into glucose and galactose for easy absorption by human body. When the human body lacks lactase, lactose cannot be absorbed by the small intestine and enters the large intestine directly, where it is fermented and decomposed by some enzymes in the large intestine, producing a lot of gases, such as carbon dioxide, hydrogen and methane, as well as short-chain fatty acids and other fermentation products, which can bring about intestinal tinnitus, flatulence, abdominal pain, diarrhea and colic. In adults, lactose intolerance occurs, such as diarrhea when drinking milk. In babies, lactose intolerance can cause malnutrition and persistent diarrhea, which can seriously affect growth and intellectual development.