If a child is lactose intolerant, parents can go to a maternity and baby store to pick a lactose-free infant formula. Lactose intolerance is due to a deficiency or insufficient activity of lactase in the small intestinal mucosa, which results in the inability to completely digest and break down the lactose in breast milk or cow's milk. Common symptoms may include weeks of diarrhea, bloating, and abdominal pain. Primary lactose intolerance is usually caused by genetic factors, while secondary lactose intolerance is generally caused by gastroenteritis. When a child exhibits the aforementioned symptoms, parents need to improve the child's diet and switch to a lactose-free infant formula, which not only ensures the child's nutritional intake but also alleviates the condition of lactose intolerance. If necessary, they should visit a formal hospital for relevant examinations and treatment.