If you have an allergic reaction to one type of nut, you might be tempted to avoid eating all others. After all, symptoms like itchy lips, hives and face swelling aren't pleasant, and food allergies can be life threatening in the worst-case scenarios.
But now, a new study finds that just because you're diagnosed with a nut allergy doesn't necessarily mean you're allergic to it. In the research published in Annals of Allergy, Asthma and Immunology, at least half of people with a diagnosed nut allergy do not show allergic symptoms to other types of nuts—even when tests show that they are allergic. And nearly all of the people with allergies to peanuts—which are technically legumes—were able to safely eat tree nuts like almonds, walnuts and Brazil nuts, even though tests had suggested they might be problematic.
Researchers looked at data from 109 people who had tested positive for a tree nut allergy, according to blood and skin tests done in the past eight years. For example, if a person knew they were allergic to almonds and also tested positive for a cashew allergy—but had never eaten a cashew in her life—researchers fed her small amounts of cashews every 15 to 20 minutes to see if there was a reaction. (Don't try this at home: doctors were standing by with life-saving medication, if necessary.) They looked for serious reactions, like hives or trouble breathing, but found that 50% of people displayed no allergic reaction, even though blood tests suggested otherwise.
That may be because some people have antibodies that react in blood or skin-prick tests, but they don't necessarily have any symptoms when they eat the food. In other words, they're sensitized to the allergen.
While most people with peanut allergies were able to eat tree nuts, that wasn't true for everyone. “Some of the individuals tested in the study had peanut allergies but never tried tree nuts, and when they tried them, they turned out to be allergic,” says Dr. Christopher Couch, an allergist-immunologist and lead author of the study.
"If a person thinks they have a nut allergy, I suggest they speak to their doctor about the symptoms and why they are suspicious,” says Dr. Scott Sicherer, a professor of pediatrics, allergy and immunology at the Mount Sinai Icahn School of Medicine. An allergist-immunologist can use a person's medical history and blood tests to decide if a nut allergy is really the problem, he says.