Ask the Dietitian – Immediate and Delayed Allergic Reactions

Question: What is the difference between immediate and delayed allergic reactions? We are trying to get to the bottom of what foods are causing my son’s allergic reactions and I think that he may be having a delayed reaction to something.

Answer: Immediate allergic reactions, also known as IgE reactions, occur within a few moments of exposure to an allergen to up to two hours, so it is easy to identify which food is causing the reaction.

Delayed allergic reactions (which are non-IgE) can happen anywhere from two to 72 hours after exposure to an allergen, or longer. This can make it difficult to pinpoint what is causing a reaction. Plus, there are no specific lab tests to identify non-IgE allergies so the only way to know if a food is safe or not is through trial and error. It might be helpful to keep a food journal of exactly what your son eats and when. Then you can look for patterns over time, and hopefully figure it all out!

If you’re still having trouble identifying the problem foods, your doctor may recommend an elimination diet. With an elimination diet, all foods are taken out of the diet and an elemental formula, such as Neocate and/or E028 Splash, is the sole source of nutrition. This period allows the symptoms to resolve and sets up your “baseline”. After a few weeks, foods are added back to the diet one at a time. Since the reactions are delayed, you should wait a few days after each food introduction to see if symptoms return. If no symptoms occur, you move on to the next food. If symptoms do occur, you can add this food to the no-no list and continue with this process (remember that there may be multiple foods responsible so you have to contrinue with the process of trying foods one at a time).

Published: 01/30/2011
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