Introduce one new food at a time, Baby rice or pureed vegetables are best to start with: If he or she rejects a food or develops diarrhea, vomiting, or a rash, avoid the food for a few weeks. Gradually reduce milk intake, and use only special formula or breast milk under medical supervision until your baby is 1 year old. If he is still allergic to breast milk, DO NOT DELAY, LET YOUR DOCTOR CONFIRM IF YOUR BABY IS ALLERGIC TO LACTOSE OR SUCROSE, PROTEIN AND ANY OTHER SPECIFIC FOODS, SO THAT THE RECACTION TO FOOD WON'T AFFECT YOUR BABY'S GROWTH. in many children, no specific cause can be found, however, some food allergies are severe, and lifelong(for exaple: peanuts)