It is possible that some people can handle small amounts of the foods, which they are allergic to without much difficulty. While others are so sensitive that they react to even the smallest traces. Most reactions are fast, usually within a few minutes of the food entering the body and can occur up to two hours later. In some cases the reaction does not occur for up to forty-eight hours later. These are the ones that are difficult to identify.
Some allergens are easy to identify because the reaction is immediate.
In other cases you may be asked to keep a diary of what you ate and the times. After a while a pattern will begin to show what the problem foods are. In some cases allergy testing may need to be done. The most common are the skin test where food allergens are placed on the skin and swelling or itching will occur if you have a reaction. This test allows for a few drops of a person s blood to be mixed with the allergens and then analyzed for signs of a reaction.