How can I find out whether my child is allergic to something in her diet?
Food allergies are reproducible. The allergic reaction should occur every time the allergen is consumed in similar quantities. When a suspected reaction occurs, read the ingredients of everything your child has eaten over the past few hours prior to the reaction.
Look first for ingredients that are new to your child's diet. If the food you suspect is sometimes tolerated without any reaction, it is extremely unlikely to be the culprit. If the suspected food is an ingredient in many foods eaten throughout the day, such as milk, egg or wheat, the reactions can be chronic and harder to identify. In this case, you should consider allergy testing.
Allergy testing can be done by testing the blood or skin. Blood testing can be ordered by any physician, while skin-prick testing usually is done by an allergist. With skin-prick testing, an extract of the food is applied to the skin, and the skin is pricked with a skin test device. A hive, or rash, appears around the prick within a few minutes if the test is positive.
With both forms of testing, a negative test makes it unlikely that the child has the allergy. However, when either test is positive, there is only a 50 percent chance that the allergy is present. The only way to confirm the suspected allergy is by eliminating the food to see if the symptoms go away and then re-introducing the food (under medical supervision) to see if the symptoms recur.