Food allergy is defined as adverse reactions toward food mediated by aberrant immune mechanisms. Therefore, an allergic response to a food antigen can be thought of as an aberrant mucosal immune response. Food allergy most often begins in the first 1~2 years of life with the process of sensitization by which the immune system responds to specific food proteins, most often with the development of allergen-specific immunoglobulin E (IgE). Over time, most food allergeies are lost, although allergy to some foods is often long lived. The most important allergen sources involved in early food allergy are milk, eggs, peanut, soybean, meat, fish and cereals. Milk allergy seem to be associated with casein and whey protein. Important features of proteins as allergenicity are size, abundance and stability. Strategies for the prevention of milk allergy is breast-feeding, partially hydrolysised infant formula, using of probiotics, immune components in milk, preparation of low allergenicity milk protein and allergy therapy (immune therapy).