A tree nut allergy is a potentially deadly type of food allergy. It involves an allergic reaction triggered by the proteins in tree nuts. Tree nuts are the hard, edible seeds of some trees. Tree nuts and their products (e.g., nut oils) are a common food type and are also found in a number of nonconsumable products ranging from shampoos to topical creams.

The most common tree nuts are:

• Almonds
  
  
• Beechnuts
  
  
• Brazil nuts
  
  
• Cashews
  
  
• Chestnuts
  
  
• Filberts
  
  
• Hazelnuts
  
  
• Hickory nuts
  
  
• Macadamia nuts
  
  
• Pecans
  
  
• Pine nuts (Pignoli nuts, Pinion)
  
  
• Pistachios
  
  
• Walnuts­­

It should be noted that not all foods with the word “nut” in them are actually tree nuts. For example, peanuts are actually legumes (bean) and are not a type of nut, though people with tree nut allergies may be allergic to peanuts as well.

In addition, nutmeg is a spice, water chestnuts are fruits, ginger nut is a type of cookie and coconut is a fruit. However, people who suffer from severe tree nut allergies may in rare instances experience allergic symptoms when consuming nutmeg or coconut.  

According to the American Academy of Allergy, Asthma and Immunology (AAAAI), about 3 million Americans are allergic to tree nuts and/or peanuts. These allergies are severe enough to kill more than 100 people every year.

Individuals allergic to tree nuts who have been exposed to tree nut proteins will usually begin to experience symptoms immediately, though they can also begin several hours later. Symptoms can also recur hours after the initial reaction subsides. Symptoms typically include swelling, hives, itchiness, redness, nausea and stomach pain. Severe reactions can result in anaphylaxis, leading to life-threatening anaphylactic shock, which includes difficulty breathing and a dangerous drop in blood pressure.

Tree nut allergies can trigger an allergic cascade that includes the following steps:

• The immune system responds when a tree nut protein enters the body. This usually occurs by eating tree nuts, their components or traces of tree nuts. However, in some individuals it can also occur through skin contact or even inhaling tree nut fumes (usually released during cooking).
  
  
• The immune system reacts by misidentifying tree nut proteins as a dangerous substance. To combat the perceived threat, the body triggers the release of immunoglobin E (IgE) antibodies.
  
  
• The IgE antibodies trigger the release of histamines and other chemicals from mast cells and basophils. The histamines and other chemicals are responsible for the most common allergy symptoms.

Tree nut allergies can be triggered by a very tiny amount of tree nut protein – much less than for any other type of food allergy, except peanuts. Some highly sensitive individuals can have an allergic response simply by kissing or having skin-to-skin contact with another person who has recently eaten tree nuts.

Thermal and chemical treatment of tree nuts (as occurs with cooking or processing) is not effective at reducing the strength of tree nut allergens. This differs from other food allergies, in which cooking or chemically treating foods tend to reduce the allergic response triggered.

The effect of tree nuts on young children, especially infants, is still being studied. Some research suggests that breastfeeding mothers who eat foods associated with allergies (including tree nuts, peanuts, milk, eggs and many others) may pass on exposure to these allergens through their milk. These studies seem to suggest that some infants become sensitized to tree nut allergens at an early age. Conversely, other research has found evidence that the transmission of food allergens can be beneficial, allowing infants to build up a tolerance to the allergen that is likely to prevent future allergic reactions. More clinical research is needed before the medical community conclusively reaches a consensus on this issue.