If the baby is lactose intolerant and does not have frequent bowel movements and it does not affect their growth and development, then no special treatment is needed. If there is frequent diarrhea and slow weight gain, then an adjustment in diet is necessary. If there is significant acute diarrhea accompanied by dehydration, we should initially rehydrate the infant either intravenously or orally to correct the dehydration. At the same time, you can start with some lactose-free formula and, after the diarrhea stops, gradually increase the amount of breast milk or other formulas based on the child's condition. Regardless of whatever food substitute is used, the overall principle is to not decrease the nutritional needs of the child. As solid foods are introduced and breast milk or cow's milk is decreased, diarrhea will gradually cease. If diarrhea does not subside, oral lactase enzyme preparations can also be provided to supplement lactase enzyme therapy.