Food allergy is a specific unwanted response to a particular food.
For example, most people could drink a glass of milk or eat an egg without problems, However, In a small number of people their body's immune system responds to that food unfavourably. There are many kinds of reactions to foods. Very few prevalence studies have been done. Adverse reactions to food are of the same magnitude in all age groups, and not a specific problem for infants, which is the common belief today. The prevalence of true food allergy is unknown.