About Preventing Allergies in Siblings

Published: August 25, 2010

Q. I have three children, aged 12, 7 and 18 months. My 12-year-old daughter developed peanut allergy at 2. My 7-year-old daughter had a test at 3 and wasn’t allergic to peanut. Now at age 7, she is. Why is that? And is there anything preventative I can do for my 18-month-old son?

Dr. Watson: Unfortunately, peanut allergy is increasing. A negative skin or blood test for peanut allergy in a child before they are exposed to peanut only tells you that they have not yet made any IgE, the allergic antibodies, to peanut. It does not predict the development of an allergy.

For children who have outgrown this allergy, regularly eating peanut appears to reduce the risk of the peanut allergy coming back. It is not known if this is true for children who do not have a peanut allergy. So it is difficult to know why your second child developed her peanut allergy at age 7. Was she eating peanut regularly?

For your third child, I would exercise caution because of your other children’s allergies. I would keep peanut-containing products out of the house. There are no good studies that say prevention of an allergy is possible, so I cannot make a scientific recommendation. The longer you avoid peanut exposure, the more you may delay a possible allergic reaction.

If you decide to have your son tested, I would recommend doing so before school, while he’s under your supervision. If the test is negative, then you will need to decide whether you are comfortable with continuing to avoid peanut versus feeding it to him regularly. I wish I knew the right answer. I do not, but neither does any other allergist. This is an area of heated debate.

We welcome your question to Allergic Living’s Ask the Allergist. Thank you for understanding that the specialists aren’t able to answer every question received.

Dr. Wade Watson is a pediatric allergist and Professor of Pediatrics at Dalhousie University. He is also the head of the Division of Allergy at the IWK Health Centre in Halifax.

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