It is well established that food antigens can pass from mothers to infants via the breast milk. Bovine-beta-lactoglobulin has been detected in several breast milk samples from mothers with regular intake of cow's milk. Healthy breastfed infants can produce IgG antibodies against cow's milk protein and in infants at risk for atopic disease specific IgE antibodies were found before cow's milk based infant formula was introduced into the diet. However, several clinical studies in infants at risk for atopic disease indicate that exclusive breastfeeding decreases the incidence of atopic disease. The protective effect of breastfeeding is only relative and it is uncertain, how long protection lasts. Sensitization to food antigens may occur already in utero, because infants whose mothers avoid common allergenic foods during the whole pregnancy and then during the lactation period have a lower incidence of atopic eczema than infants whose mothers are on an unrestricted diet. Avoidance of common allergenic foods only during the last trimester of pregnancy had no effect, because the fetus is capable of forming IgE immune response.