Lactose intolerance in babies is due to low lactase secretion in babies, and babies cannot fully digest and break down the lactose in breast milk or cow’s milk, which leads to non-infectious diarrhea in babies. There are generally two causes, one is congenital lactase deficiency, this is caused by a genetic defect abnormality, so it is usually difficult to relieve and will persist, this condition is very rare. The second is secondary lactase deficiency, this usually takes 0.5-2 months, when the baby can secrete sufficient amount of lactase, the symptoms of diarrhea will be relieved.