Unlike peanuts, which are really legumes (in the bean family), tree nuts are
really nuts. Tree nuts include almonds, Brazil nuts, cashews, hazel nuts, hickory
nuts, macadamia nuts, pecans, pine nuts, pistachios, and walnuts. As
opposed to peanuts, which grow in the ground, tree nuts, as their name
implies, grow on trees.

In food allergy circles, most people lump together peanuts and tree nuts.
Botanically speaking, associating peanuts with tree nuts is absurd. Allergically
speaking, however, the association makes a lot of sense. Following is a list of
similarities:

1. Like peanuts, tree nuts can cause severe allergic reactions.
2. Tree nuts are capable of causing severe reactions with minute exposures.
3. Peanuts and tree nuts tend to travel in the same circles — baked goods, ethnic foods, candies, and ice creams are the most common causes of accidental tree nut exposures.
4. Tree nut oils and extracts all contain the allergenic proteins, so you must avoid the oils and extracts, too.

In studies of fatal food allergic reactions, tree nuts rank second only to peanuts.

Even though tree nuts and peanuts are botanically unrelated, people with tree nut allergy often have peanut allergy, and vice versa. Several studies show that 30 to 40 percent of people with peanut allergy also develop tree nut allergy. We allergists used to struggle to explain the link between peanut and tree allergy, and we thought it was most likely due to the fact that peanuts and tree nuts are both just very potent allergens. New research, however, has uncovered actual structural similarities between peanut protein and many of the tree nut proteins.

At this point, you’re probably wondering, “If I have a peanut allergy, should I avoid tree nuts?” The short answer is “Yes.” For a longer answer, discuss with your doctor the pros and cons of avoiding tree nuts. In my clinic, we recommend that patients with peanut allergy avoid tree nuts for the following three reasons:

1. Peanuts and tree nuts are all too often processed together or at least near enough to one another to pose sufficient risk.
2. Manufacturers often use peanuts as a substitute for tree nuts, because peanuts are cheaper.
3. In young children with peanut allergy, staying away from tree nuts may help prevent the child from developing a tree nut allergy.

For those with a tree nut allergy, many forms of peanut can be safe, especially major brand peanut butter and some candies. Be careful though; dry roasted peanuts are often tree-nut contaminated, and a gourmet peanut butter may have shared equipment with almond or cashew butter. In my clinic, we encourage patients with tree nut allergy to avoid peanuts, as well, generally for the same reasons we tell our peanut-allergic patients to avoid tree nuts.

Related posts:

1. Peanut Allergy : Deciphering the mysteries of peanut oils
2. Food Allergens : Nut
3. Peanut Allergy : Choosing a peanut-lite restaurant
4. Peanut Allergy : Acknowledging the deadly risk
5. Peanut Allergy : Uncovering peanuts in candies