Tree nut allergy is one of the most common types of food allergy. Tree nuts include almonds, Brazil nuts, cashews, chestnuts, hazelnuts, macadamia nuts, pecans, pine nuts (pignolia nuts), pistachios, and walnuts. People with tree nut allergy are seldom allergic to just one type of nut, and are therefore usually advised to avoid all tree nuts.
Tree nut allergy is distinct from peanut allergy. Peanuts are considered legumes whereas a nut is a hard shelled fruit of certain plants. A person with peanut allergies may not necessarily also be allergic to tree nuts, and vice versa.
Any products with labels stating "may contain traces of tree nuts" or "processed in a plant that process tree nuts" are considered unsafe.