Q: I understand my daughter being allergic to peanuts and soybeans – as they are both legumes. But following a reaction, she’s now confirmed allergic to tree nuts as well. Is this coincidence or are nuts and peanuts related?
Dr. Sharma: This reaction is not a coincidence. In fact, about one-quarter to one-half of people with peanut allergy also have an allergy to tree nuts.
Some of this relates to “cross-reactivity.” This occurs when the immune system “sees” peanut and tree nuts as alike because of similarity in their protein structures that bind to IgE allergy antibodies.
This cross-reactivity exists between peanut IgE and and pecan, almond, Brazil nut and hazelnut.
Tree Nut, Peanut ‘Co-allergy’
The likelihood of “co-allergy” between peanut and tree nuts seems to increase as children get older.
I should note, however, that positive skin or blood tests to cross-reactive foods do not necessarily confirm a “co-allergy.” There quite often are false positives. For example, it’s common for someone with one legume allergy (like peanut) to have positive skin and blood testing to multiple legumes. But clinical cross-reactions to those other legumes are rare.
In one study, 31 percent of children with a peanut allergy had a positive skin test to soy. Yet only 3 percent had a clinical reaction to soy when consuming it.
Dr. Sharma is an allergist, clinical researcher and Assistant Professor of Pediatrics. He is Associate Chief of the Division of Allergy and Immunology at Children’s National Medical Center in Washington D.C. and Director of the Food Allergy Program.Submit a Question View all posts by this medical expert.