The more complete the hydrolysis process the less allergenic the milk. But extensively hydrolysed formulas are very expensive and tend to have an unpleasant taste which is poorly tolerated by older infants. Soya milk formulas now seem to have fallen from favour in food allergy prevention as soya is a potential allergen. Potential food allergens in the diet, such as cows milk, soya, citrus and wheat , should be avoided for the first year of life , with eggs, peanuts and bony fish being introduced only after 2-3 years of age . Factors that promote allergic sensitization such as maternal cigarette smoking, air pollution and viral illnesses should be avoided whenever possible.
Avoidance is easy to prescribe but in reality is very difficult to implement.
Therefore the strictness of the diet often depends on the severity of the food allergy symptoms. Most food allergic children eventually tolerate milk, eggs and vegetables but usually remain allergic to fish and nuts.