Lactase is usually effective in about 2-3 days, but it cannot be generalized, depending on the individual’s constitution. Lactase is present on the mucosal surface of the small intestine and is able to digest lactose in milk. If lactose is not hydrolyzed and digested by lactase in the small intestine, it will be defeated by intestinal bacteria when it enters the colon, producing a lot of gas and causing hyperosmolar diarrhea, i.e. lactose intolerance. In addition, diarrhea and other causes can damage the lactase enzyme on the small intestinal mucosa, causing accumulation of food and indigestion. Lactase is commonly used to treat lactose intolerance, diarrhea, indigestion, heartburn, and irritable bowel syndrome, etc. The results can be seen in about 2-3 days and the course of treatment is about 1-2 weeks. During lactase treatment, pay attention to reduce the amount of breastfeeding, mainly lactose-free formula, and gradually stop lactase when the symptoms are completely recovered. Lactose-free formula needs to be stopped gradually in order to ensure adequate nutrition for the baby.