If you are allergic to one type of tree nut, avoiding all others may not be necessary, a new study suggests.

The study, published Monday in Annals of Allergy, Asthma and Immunology (ACAAI), suggests that many people are wrongly led to believe that they are allergic to all tree nuts based on a blood or a skin prick test.

Researchers “strongly suggest” that people also consider taking an oral food challenge, which involves eating tiny amounts of nuts in increasing doses over a period of time, under supervision of an allergist.

The oral food challenge is considered the most accurate way to diagnose a food allergy, researchers say.

“Too often, people are told they’re allergic to tree nuts based on a blood or skin prick test,” Dr. Christopher Couch, an allergist and lead author of the study, said in a news release. “They take the results at face value and stop eating all tree nuts when they might not actually be allergic.”

The study involved 109 people with a known allergy to an individual tree nut. They were tested for allergies to other tree nuts they had never eaten before using blood or skin prick tests. Despite showing sensitivity to other tree nuts, more than 50 per cent of those tested had no reaction to the nuts during the oral food challenge.

Tree nuts include almonds, cashews, walnuts and hazelnuts, but not peanuts.

“Previous studies suggested people with a tree nut allergy, as well as those with a peanut allergy, were at risk of being allergic to multiple tree nuts,” Dr. Matthew Greenhawt, chair of the ACAAI food allergy committee and study co-author, said. 

“We found even a large-sized skin test or elevated blood allergy test is not enough by itself to accurately diagnose a tree nut allergy if the person has never eaten that nut. Tree nut allergy should only be diagnosed if there is both a positive test and a history of developing symptoms after eating that tree nut.”