Q: I understand my daughter being allergic to peanuts and soy beans – as they are both legumes. But following a reaction, she’s now confirmed allergic to tree nuts. Is this coincidence or are nuts and legumes related?
Dr. Sharma: This is not coincidence, as about one-quarter to one-half of people with peanut allergy  also have an allergy to tree nuts.
Some of this is related to “cross-reactivity,” where the immune system “sees” peanut and tree nuts  as alike because of similarity in the parts of their protein structures that bind to IgE antibodies.
This cross-reactivity exists between peanut IgE and pecan, almond, Brazil nut and hazelnut.
The likelihood of “co-allergy” between peanut and tree nuts seems to increase as children get older. I should note that positive skin or blood tested to cross-reactive foods do not necessarily confirm a “co-allergy.”
For example, it’s common for someone with one legume allergy to have positive skin and blood tests to multiple legumes, but clinical cross-reactions to those other legumes are rare.
In one study, although 31 percent of children with a peanut allergy had a positive skin test to soy, only 3 percent had a clinical reaction to 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. He co-authors “The Food Allergy Experts” column in the American Edition of Allergic Living  magazine. Questions submitted below will be considered for answer in the magazine.