Tree nuts are prized by some for their healthy fats but to others they spell trouble. About three million Americans have allergies to tree nuts and/or peanuts, according to the American Academy of Allergy, Asthma and Immunology (AAAAI).

Almonds, walnuts, cashews, pecans and other nuts typically cause symptoms, including nausea, swelling, itchiness, hives, redness, stomach pain, wheezing, tingly tongue and runny nose. In up to 100 cases per year, individuals suffer a more severe and deadly reaction, called anaphylactic shock.

Tree nut allergy, like other food allergies, sometimes show up in childhood but may develop later in life. Some individuals may have intolerance, rather than allergy, where they experience digestive trouble hours or a day after eating nuts. I have tree nut intolerance, and develop nausea and stomach pain every time I eat nuts in any form.

Those with this type of allergy need to be wary of all kinds of tree nuts. Many need to avoid peanuts, even though they are legumes not nuts. Individuals with tree nut allergy probably should avoid seeds as well (e.g. sesame, poppy, pine nuts, sunflower). This is true because tree nuts are just large edible seeds. There is no cure for this allergy other than total avoidance.

Not all foods with the word “nut” in them are tree nuts. Examples include pine nuts and peanuts as well as nutmeg (spice), water chestnuts (fruit) or coconut (fruit). In rare cases, individuals with nut allergy may have reactions to nutmeg and coconut.

Tree nut allergy requires constant vigilance when grocery shopping or dining away from home. Only a trace amount may trigger a reaction. Checking and rechecking food labels is necessary because sometimes food processors change the ingredients in items.

Common foods that contain tree nuts include: marzipan (nut paste), nougat, nut butter, nut oils, nut meal, nut paste, nut extract (almond extract), candy, crackers and many other processed foods. Cross-contamination of foods in factories that produce items with nuts has long been a concern. Since January, 2006, food manufacturers have been required to list tree nut ingredients on packaged foods.

If you suspect you have tree nut allergy or intolerance, keep a daily food journal for several weeks and note symptoms associated with eating certain foods. You may want to try an elimination diet where you do not eat nuts for several weeks to see if symptoms persist. Or see an allergy specialist who may identify specific food allergies through a blood test. Some other conditions, such as irritable bowel syndrome or gastrointestinal problems, can be mistaken for nut allergy or intolerance.