Question regarding peanut allergy and tree nut allergy cross reactivity...


I have a parent who knows her child is peanut allergic and has been told to avoid tree nuts also and wants to know several years later, if tree nuts can be added to his diet if serology (sIgE) and skin testing is negative, and if we can prove on oral challenge that it is tolerated?


Usually we ask peanut allergic patients to avoid tree nuts because of the chance of cross reactivity and possibility of an anaphylactic reaction even with first exposure in a tree-nut naive patient. However would you offer oral challenge to all tree nuts for this case of a peanut allergic patient which negative testing to tree nuts, which seems a lengthy process to cover all tree nuts?!


The risk of cross contamination amongst the tree nuts makes it necessary to check that he is not allergic to any and all tree nuts.


What is the risk of cross contamination of tree nuts and peanut, ie in a patient peanut allergic who consumes tree nuts, are they at risk of peanut traces in the tree nuts? Ie. Do the plants manufacture peanuts and tree nuts at the same area? And if that is the case, you would not only not want peanut allergic patients to avoid tree nuts for the chance of trace peanut, but could it go the other way that tree nut allergic patients need to avoid peanut even if not allergic to peanut, because of the risk of traces of tree nut in peanut butter etc for example?


Thank you for your recent inquiry.

I have copied for you below an inquiry to the Ask the Expert site similar to yours that was answered by Dr. Hugh Sampson. As you can see from Dr. Sampson's response, he recommends children with peanut allergy avoid the ingestion of tree nuts until they are "older." Then he often considers testing to tree nuts with consideration of introducing them into the child's diet. The decision to do so may vary from physician to physician depending on how comfortable they are with performing food challenges when skin tests are negative.

However, I am not an expert in this field and therefore am asking Dr. Scott Sicherer, an internationally known expert in food allergy in children, to share his thoughts with us about the issues you present.

As soon as I hear from Dr. Sicherer, we will forward his comments to you.

Thank you again for your inquiry.

Previous inquiry dated 5/7/2008
Avoidance of peanuts in a patient with tree nut allergy
I ask this question as a pediatrician (in practice almost 10 years) and as a parent.

I always felt fairly knowledgeable about food allergy as a general pediatrician UNTIL one of my children had an anaphylactic reaction to cashews. Since then I have become much more knowledgeable about food allergy and feel that I give much better advise.

I need your help in devising recommendations for families whose children test positive for nut allergy... if a patient tests positive for allergy to a single tree nut such as a cashew, but negative for other tree nuts and peanuts, do they JUST avoid cashew or should they avoid ALL tree nuts and peanuts (or avoid tree nuts but enjoy peanuts)?

Interestingly, I was at a party this weekend where the child has a cashew allergy. The house was deemed "nut safe" by the hosts. There were about 20 bowls of peanuts mixed with M & M's (which are also made, I believe, in a factory that also processes nuts - I'm not sure if just peanuts) scattered throughout the house. To me this really highlighted the topic.

I was glad my daughter with cashew allergy was not there. WE AVOID ALL NUTS, INCLUDING PEANUTS, AT THE RECOMMENDATION OF OUR VERY GOOD ALLERGIST, DR. ACETA. I know the other family can do what they want with their own children, but I'm sure their pediatrician told them its okay to just avoid tree nuts and peanuts are fine.

I am asking the question in general. I understand that with more information (grade of allergy, hx of anaphylaxis or not, etc) your answers could be modified.

In answering your question, first I would like to quote Dr. Hugh Sampson, who is a world recognized expert on food allergy. He responded to a similar question submitted to us a few months ago. The question was a little different in that he was asked whether or not a patient who is known to have a peanut allergy should avoid tree nuts. His answer, taken from our web site, is seen below:

" If you have a toddler who is allergic to peanut supported by history and skin testing, should they empirically avoid tree nuts despite there different protein structures since we know tree nuts might be sensitizers- and vice versus, tree nut allergic....avoid peanut?"

Dr. Sampson's Response:
"If a toddler has a clear-cut, recent reaction to peanut and a positive skin test, I generally tell the parents that they should eliminate peanuts and tree nuts from the child's diet. [I also obtain a peanut-specific IgE level so that I can get some idea of whether this toddler may fall into the 20% of young children who will outgrow their peanut allergy] There is little evidence to support the notion that tree nuts 'cross-react' with peanuts and therefore avoidance for this reason seems unjustified. However, two other factors that support tree nut avoidance must be considered. (1) Studies indicate that about 35% of American toddlers with peanut allergy will have [or develop] concomitant tree nut allergy. (2) In a young child, it is very confusing to distinguish the difference between peanut and 'safe' tree nuts, since many adults refer to both as nuts and are unaware of situations where peanuts may be included with specific tree nuts. We have seen too many accidents where a child receives peanut-containing products because of misidentification, cross-contamination, or substitution with some peanut product. Consequently we think it is safer to avoid tree nuts until the child is old enough to understand the nuances of avoiding peanut contaminated foods. We often will skin test the child to various tree nuts [and obtain nut-specific IgE if the skin test is positive] so that the parents will know whether the child is likely to experience an allergic reaction if the child inadvertently ingests a tree nut-containing food."

Phil Lieberman, M.D.

We have received the response from Dr. Sicherer which is posted below. Thank you again for your inquiry, and we hope this response is helpful to you.

Phil Lieberman, M.D.

Response from Dr. Scott Sicherer:
There are a lot of issues here about risks of developing a new allergy to a tree nut and about whether a person with a peanut and or a particular tree nut allergy could or should be cleared (by testing/challenge) to add otherwise “safe” nuts when cross contact issues arise (processing) or misclassification (is that a Brazil nut or a cashew?).  These are issues that I work individually with families. I agree with the prior responses given to aspects of the related queries.   It is often easier to say to avoid “peanut and tree nut” but more and more families are interested in adding some or all of them.  It is easy to get peanut that has no tree nut contact issues.  It is harder among tree nut products (e.g., allowing to eat walnut if person is allergic to cashew).  I am not aware of a comprehensive assay based study to try to delineate exact risks of cross contact.  The age, severity, family preferences, etc., all come into play.
I probably approach adding tree nuts more readily when a family is only avoiding peanut, compared to when a child has already had a known tree nut allergy because, again, of the cross-contact concerns.
For a family that wants to embark on adding tree nuts, almond is often my first step.  There are a number of cereals and butters, even drinks, that are just almond.  I also have families that want to crack open shelled nuts, which is another direction of offering, that I pursue when requested.
When it is likely that most or all nuts will be tolerated, I sometimes do several nuts at the same time for a food challenge (moving along from eating one type then another, etc).  This cuts down on the number of visits for a challenge, although if there are symptoms we might not know which nut type was the problem.  I might group the more available nuts (free from cross contact or more popular in products)  or the ones that tested more likely to be tolerated as groupings.  For example, perhaps almond, hazel, walnut and pecan in one day and then cashew/pistachio another day.  Note also that some nuts have some homologous proteins and may be paired for that reason.
My impression is that a majority of my patients with peanut or a tree nut allergy prefer to avoid the entire groups.  However, most with a tree nut allergy want to continue peanut (I remind them also about cross-contact, using major brands, etc).  They need to watch out for example in stores grinding peanut butter where they also grind cashew butter.
When the child is older, more with a peanut allergy begin to ask to allow certain nuts, and I go with that if they wish after a risk/benefit review.  Relatively few with a serious nut allergy want to eat other nuts, but when they strongly desire, I work with them.  I always suggest they research what they would actually be able to buy/use if we proceed to evaluate for tolerating the additional foods.
Scott H. Sicherer, MD
Professor of Pediatrics
Jaffe Food Allergy Institute
Mount Sinai School of Medicine
New York, NY

Ask A Question

Healthcare Professionals: If you can’t find what you are looking for, please send us your question.

Ask now

AAAAI - American Academy of Allergy Asthma & Immunology