Tree nut allergies are one of the most common and fast-growing types of food allergies in North America today.
When someone with a tree nut allergy ingests their allergen, even a trace amount, that person is at risk of a severe allergic reaction, called anaphylaxis. An anaphylactic reaction includes more than one of the body’s systems, such as the respiratory tract, gastrointestinal tract, the skin and cardiovascular symptom.
Symptoms of an allergic reaction include tingling in the mouth, swelling of the tongue and throat, itchy skin or hives, difficulty breathing, abdominal cramping and vomiting. In a severe anaphylactic reaction, a person may experience a drop of blood pressure, loss of consciousness and even cardiac arrest and death.
One of the issues in managing tree nut allergies is that reaction symptoms can vary greatly. A person may have minor symptoms on one occasion, but anaphylaxis on a next exposure.
Because tree nut allergy reactions can be severe, it is important that a person with this allergy carry an epinephrine auto-injector (EpiPen or Twinject) with them at all times. Research has shown that a small number of people (about 9 per cent) may outgrow their tree nut allergies.
In Canada, 2009 statistics show that 1.14 per cent of the population is allergic to tree nuts, while in the United States 1.1 per cent of children have the allergy and 0.5 per cent of adults. Tree nut allergy is on the rise: the 2008 telephone survey in the U.S. that found 1.1 per cent of children are allergic to nuts, compare that to just 0.2 per cent of children reported as allergic to nuts in 1997.
More on Tree Nut Allergy Statistics 
Next Page: What is a Tree Nut?
What is a Tree Nut?
Tree nuts are not just one allergen, but in fact a group of allergens. In Canada, for food labeling purposes, the following are considered tree nuts:
In the United States, the list is longer. It includes:
Macadmamia nuts/Bush nuts
Pine nuts/Pinon nuts
Next Page: What is Not a Nut?
What is Not a Nut?
While coconut is considered a tree nut when it comes to food labeling purposes in the United States, it is not, strictly speaking, a nut. Rather, it is the fruit of a palm tree.
Most people with tree nut allergies are able to eat coconut. However, it is possible to be allergic to coconut. Speak to your allergist about whether coconut is safe in your diet.
People often refer to peanuts as nuts, but peanuts are in fact legumes. While many people are allergic to both tree nuts and peanuts, it’s possible to be allergic to one and not the other. Nutmeg and water chestnuts are not nuts.
Risks with Peanuts
Those who are allergic to tree nuts are often advised not to eat peanuts because of the risk of cross-contamination during the manufacturing process, with nuts and peanuts on the same equipment. If you have a tree nut allergy, talk to your allergist about whether you should also be avoiding peanuts.
While tree nuts and peanuts are not relatives, studies show that one-third to half of people with peanut allergy also have a nut allergy.
Link to Pollen Allergies
For some people, eating nuts such as almonds, hazelnuts and walnuts can set off a tingly, itchy sensation in the mouth, lips or throat. This may not be a true allergy, but in fact, something called oral allergy syndrome  (OAS).
OAS is a reaction to foods including fruit, vegetables, nuts, spices, legumes and seeds that actually stems from pollen allergies. The structure of some of the proteins in the pollens of birch and alder trees, grass and ragweed are so similar to the proteins in related foods that some people’s immune systems can’t tell the difference. If the birch tree gives you sneezing and congestion, for instance, it’s possible that an apple, carrot or hazelnut might make your mouth itch.
It can be difficult to figure out if you’re having an actual allergic reaction to a food, which can cause anaphylaxis (the serious form of reaction) or if it is OAS. While symptoms for the latter condition are usually milder, Allergic Living strongly suggests a visit to an allergist if you are reacting to nuts of any kind.
See: OAS – A Life Without Fruit 
Next Page: Why is Tree Nut Allergy on the Rise?
Why is Tree Nut Allergy on the Rise?
No one knows for certain why people have more allergies (including nut allergies) today than they did in the past. One theory that has gained prominence is the hygiene hypothesis.
This hypothesis states that kids growing up in industrialized countries are not exposed to the level of germs, infections and parasites as kids who grow up in less clean or modern environments. (Livestock farms, for instance, have been shown to protect against allergies, which is known as the “Farm Effect ”.)
The idea is that the immune system needs these exposures to develop properly, and without them, it is underworked – and begins to develop antibodies to otherwise harmless substances, such as peanuts.
Other theories that attempt to explain a rise in food allergy include insufficient vitamin D, food processing (ie: roasting and emulsification of peanuts for peanut butter, rather than fried or boiled peanuts), and the delay of exposure to the allergen in infancy.*
*Source: 2010 FA primer. JACI
Is There a Cure?
Currently, there is no cure for tree nut allergy. Scientists are working on ways to “desensitize” patients to some allergens, including peanuts, milk and egg. The most researched and talked about form of desensitization at this point is called oral immunotherapy (OIT).
In this treatment, an allergic child consumes gradually increasing amounts of his or her allergen in an effort to retrain the immune system. Doctors have been able to show some success using this method.
While researchers believe oral immunotherapy would work tree nuts as well, this has not been studied to date.