There is a well supported notion that exclusive breast feeding prevents development of food allergies in infants. However, this rule, just like any other has exceptions. Even exclusively breast fed infants can develop food allergies. The most common culprits are peanuts and cow's milk protein. Egg and wheat proteins can also cause a problem. This happens when nursing mothers use products containing milk, peanuts, egg and wheat in their diet, when large particles of allergy causing proteins find their way to breast milk. Just like with any food allergy, the most common manifestation is atopic dermatitis. Some infants may develop chronic diarrhea and colic-like abdominal pain. More severe manifestations, including life threatening, are rare. The issue of indirect infant's exposure to variety of food allergens via breast milk is quite complex. There is for example evidence, that maternal consumption of peanuts during breast feeding may actually prevent sensitization of children to peanuts. Why in some mothers peanut consumption can cause allergies in babies while preventing the same in others ? There is no good answer. Obviously, something is missing in our knowledge about food allergen transmission and sensitization at very early age.