Hi In primary lactose intolerance all milk conaining lactose like cow milk, buffalow milk, regular formula milk including mother milk should not be give as the lactose will cause diarrhea and lactose free milk formulas and lactose free food preparations advised completely and this condition is rare. Secondary lactose intolerance occurs in situations with any type of diarrhea due to loss of intestinal villae which contain lactase enzyme which is resposible for the digestion of lactose. In this condition lactose free milk is advised for a specific duration till the villae generation occurs and there after regular milk can be given. If your child is having primary lactose intolerance complete lactose free milk should be given whereas if it is secondary one lactose free milk for approximately for 4 to 8 weeks,thereafter breastfeeding can be restarted.