Tree nut allergy is one of the eight most common food allergies, affecting roughly 0.5 to 1% of the U.S. population. Tree nuts grow on trees, whereas peanuts grow underground and are considered legumes. Tree nuts include almonds, Brazil nuts, cashews, hazelnuts, pecans, pistachios and walnuts.
An allergy to one tree nut does not necessarily mean an individual is allergic to other tree nuts, but certain tree nuts are closely related, including cashew with pistachio and pecan with walnut. Even though individuals allergic to tree nuts are often allergic to more than one type of tree nut, it may be appropriate and safe to consume certain tree nuts while avoiding others. This decision must be made after careful discussion with an allergist and should be based on multiple factors, including the age of the individual, results of allergy testing, risk of potential cross reactivity between the nuts, quality of life implications and family preferences. If an individual allergic to certain tree nuts chooses to consume other tree nuts, they should always account for the potential risk of cross contamination (the introduction of trace amounts of the allergenic food during preparation and handling), which may or may not be clinically relevant for all individuals.
Although 30% of peanut-allergic individuals are also allergic to tree nuts, having a tree nut allergy does not necessarily mean an individual is allergic to peanuts. Individuals with tree nut allergy can also typically consume seeds without difficulty, such as sesame, sunflower and pumpkin. They also usually tolerate macadamia nut and pine nut, which are also both seeds. Although the Food and Drug Administration labels coconut as a tree nut, the vast majority of tree nut-allergic individuals also tolerate coconut without difficulty, since coconut is not truly a nut, but rather a fruit. Nutmeg, water chestnut, butternut squash and shea nuts are not tree nuts (the term “nut” does not always indicate a tree nut) and are generally well tolerated by tree nut-allergic individuals. All individuals with tree nut allergy should discuss these specific dietary considerations with an allergist familiar in the management of food allergy.
Although tree nut allergy typically starts in childhood and persists throughout life, approximately 10% of individuals may outgrow tree nut allergy over time. Based on the results of repeat allergy testing, a supervised oral food challenge can be considered if there is a favorable likelihood that the allergy has been outgrown.
Food challenges should also be considered if patients show low levels of sensitivity on skin prick or serum IgE testing that may not be considered consistent with true clinical allergy. All oral food challenges should be performed in a medical facility equipped to recognize and treat allergic reactions, with supervision by an allergist.
Reactions to tree nuts can be severe, including life threatening anaphylaxis, and individuals with a tree nut allergy should have epinephrine available at all times. With proper education, individuals with tree nut allergy can maintain a broad and nutritionally adequate diet, and good quality of life.
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This article has been reviewed by Andrew Moore, MD, FAAAAI