Allergic reactions to tree nuts are becoming more common. Walnut allergy diagnosis has been on a rapid increase now becoming a very common sensitising nut in children. Now found in 4% of children and 0.5% of adults and affects 34% of all tree nut allergic individuals (data Thermofisher). The allergenic protein in the Walnut (Jug r1 and Jug r3) is heat resistant so not rendered less allergenic when cooked. Walnut is also closely related to Pecan nut, so often these two nut allergies will occur concurrently. Walnut allergy is seldom outgrown, so persists into adult life. It has also been implicated in food-dependent exercise induced anaphylaxis and reactions can be made worse with drinking alcohol and taking aspirin related anti-inflammatory medications.

Reference: http://www.phadia.com/en/Products/Allergy-testing-products/ImmunoCAP-Allergen-Information/Food-of-Plant-Origin/Allergen-Components/rJug-r-3-Walnut/