What is Tree Nut Allergy?
A tree nut allergy is an abnormal immune response to one or more tree nuts. When a person with an allergy is exposed to certain tree nuts, their immune system launches an “attack” against the proteins in the tree nut and can even create antibodies (specifically immunoglobulin E or IgE) that target the nut proteins. This response provokes the rapid development of allergic symptoms, which can affect a variety of body systems and may be mild, moderate, or severe and life-threatening.
There are many different kinds of tree nuts, including almonds, Brazil nuts, cashews, hazelnuts, pecans, pistachios, pine nuts and walnuts. An allergy to one tree nut does not guarantee an allergy to another, but it is common for people to react to more than one tree nut. Tree nut allergies tend to develop during childhood and are usually lifelong.[1]
What are the main signs and symptoms of tree nut allergy?
An allergic reaction to tree nuts can cause a variety of signs and symptoms that range from mild to severe and may be systemic (affecting the whole body) or localized (affecting a single body part or organ). Reactions may include skin involvement (e.g., rashes, swelling, itching); eye discomfort (e.g., itchy, watery, and/or swollen eyes); respiratory difficulties (e.g., shortness of breath, coughing, wheezing, throat swelling, hoarseness); gastrointestinal issues (e.g., nausea, vomiting, cramping, diarrhea); cardiovascular changes (e.g., drops in blood pressure, increased heart rate); and neurological responses, although rare (e.g., fainting, seizures, dizziness).
Most signs and symptoms occur within minutes of exposure to tree nuts, although a delayed response of up to 2 hours is possible. Exposure to tree nuts usually happens through ingestion — skin contact or inhalation rarely causes an allergic reaction. When the allergic reaction is very severe and/or involves more than one organ system, it is called an anaphylactic reaction, which can be life-threatening without prompt treatment.[2][3]
How is tree nut allergy diagnosed?
A history of consistent allergic signs and symptoms after the ingestion of a tree nut is the first step in diagnosing a tree nut allergy. An allergist will use this history in conjunction with a physical exam to guide the choice of additional diagnostic tests.
The skin prick test is the most common diagnostic test and involves introducing the allergen into the skin through a small prick with a special tool. If IgE antibodies to tree nuts are present, the area that was pricked will swell. A swollen area 3 mm or greater in size is usually considered positive for an allergy, although some clinicians prefer an 8 mm or greater standard to decrease the chance of a false positive.[4] Blood tests that detect food-specific IgE antibodies may also be used to aid in the diagnosis.
Although these diagnostic tests are helpful, they do not predict the severity of a person’s allergic reaction, nor are they useful in people without a history of allergic signs and symptoms (given the frequency of false positives). In some cases, an oral food challenge, which consists of gradual consumption of the allergen under direct medical supervision, may be recommended to confirm the allergy.[5][6] Ideally, allergy testing is done yearly because some allergies change or resolve over time.
What are some of the main medical treatments for tree nut allergy?
Avoiding exposure to tree nuts is the first line of treatment for a tree nut allergy. This includes not eating foods that may be contaminated with tree nuts.[5]
When exposure does occur, medications can be used to treat allergic signs and symptoms. If the reaction is mild, antihistamines may be helpful, but severe reactions should be treated with epinephrine.[7] Prompt treatment is critical in preventing life-threatening reactions. For this reason, most people with a tree nut allergy are prescribed an epinephrine auto-injector and are instructed to carry it with them at all times in case of an emergency.
Have any supplements been studied for tree nut allergies?
Vitamin D supplementation is an area of ongoing research for the prevention of food allergies. Vitamin D is integral to the proper functioning of the immune system, and vitamin D insufficiency and limited sun exposure are associated with the development of food allergies in observational research.[8][9][10][11] However, whether vitamin D supplementation actually decreases the incidence of food allergies is not clear.[12]
Currently, there is also no evidence to support the use of supplements in treating tree nut allergies. However, there is ongoing research investigating the effects of certain Chinese herbs on the immune system, including their potential to dampen the inappropriate immunologic response to food proteins.[13] Of these herbs, berberine appears to be the most powerful suppressor of IgE production.[14] More research is needed to determine whether these supplements could decrease allergic reactions.
How could diet affect tree nut allergies?
Diet is the cornerstone of tree nut allergy management. People with tree nut allergies need to carefully plan their diets to avoid eating certain tree nuts. This means also avoiding foods that contain or may be contaminated with tree nuts, such as food products made in facilities that use nuts in other products, which is a potential source of cross-contamination. Most countries require that food labels clearly state whether a food contains tree nuts, and many labels voluntarily state whether cross-contamination is possible, so checking the label on all packaged food items is important for people with allergies.
Diet may even play a role in allergy prevention. Early introduction of allergenic foods (by approximately 6 months of age) alongside continued consumption reduces the risk of developing food allergies.[15][16][17]
Are there any other treatments for tree nut allergies?
Allergen avoidance and medications for accidental exposure are the mainstays of tree nut allergy management. Other treatments, such as immunotherapy and monoclonal anti-IgE antibodies, are under investigation for their efficacy in treating food allergies, including tree nut allergy. The main goal of these immune-modulating therapies is to allow a person with a food allergy to be exposed to their allergen without experiencing a severe reaction.[18][19]
What causes tree nut allergies?
Tree nut allergies are caused by an inappropriate reaction of the immune system to the proteins found in tree nuts. Normally, the immune system targets and attacks pathogens like viruses and bacteria but in the case of food allergies, the immune system identifies a certain food as an “invader” and launches an immune response against it.
This breakdown of immune tolerance is primarily driven by T helper 2 cells and often includes the production of food-specific IgE antibodies, all of which lead to a cascade of immune responses (like the activation of mast cells and release of cytokines) that cause allergic symptoms. Why the immune system reacts abnormally to certain foods in some people is not fully understood.[20]
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Frequently asked questions
A tree nut allergy is an abnormal immune response to one or more tree nuts. When a person with an allergy is exposed to certain tree nuts, their immune system launches an “attack” against the proteins in the tree nut and can even create antibodies (specifically immunoglobulin E or IgE) that target the nut proteins. This response provokes the rapid development of allergic symptoms, which can affect a variety of body systems and may be mild, moderate, or severe and life-threatening.
There are many different kinds of tree nuts, including almonds, Brazil nuts, cashews, hazelnuts, pecans, pistachios, pine nuts and walnuts. An allergy to one tree nut does not guarantee an allergy to another, but it is common for people to react to more than one tree nut. Tree nut allergies tend to develop during childhood and are usually lifelong.[1]
An allergic reaction to tree nuts can cause a variety of signs and symptoms that range from mild to severe and may be systemic (affecting the whole body) or localized (affecting a single body part or organ). Reactions may include skin involvement (e.g., rashes, swelling, itching); eye discomfort (e.g., itchy, watery, and/or swollen eyes); respiratory difficulties (e.g., shortness of breath, coughing, wheezing, throat swelling, hoarseness); gastrointestinal issues (e.g., nausea, vomiting, cramping, diarrhea); cardiovascular changes (e.g., drops in blood pressure, increased heart rate); and neurological responses, although rare (e.g., fainting, seizures, dizziness).
Most signs and symptoms occur within minutes of exposure to tree nuts, although a delayed response of up to 2 hours is possible. Exposure to tree nuts usually happens through ingestion — skin contact or inhalation rarely causes an allergic reaction. When the allergic reaction is very severe and/or involves more than one organ system, it is called an anaphylactic reaction, which can be life-threatening without prompt treatment.[2][3]
Anaphylaxis is a life-threatening allergic reaction that is rapid in onset and potentially fatal without prompt treatment with epinephrine. Food is the leading cause of anaphylaxis,[28] and anyone with an IgE-mediated food allergy can have an anaphylactic reaction. Common signs and symptoms include gastrointestinal manifestations (e.g., nausea, abdominal pain, vomiting, and diarrhea), skin reactions (e.g., itching, flushing), respiratory changes (e.g., nasal congestion, cough, wheezing, shortness of breath, sense of choking), and cardiovascular complications (e.g., hypotension, cardiovascular collapse).[29][30]
Initial symptoms usually appear within minutes following exposure to the allergen, but it is not always immediately obvious that anaphylaxis is occurring because symptoms can evolve over time. Moreover, the severity of a previous reaction does not predict the severity of future reactions. As such, if anaphylaxis is suspected, it is recommended to administer intramuscular epinephrine as quickly as possible and seek emergency medical care because symptoms can come back (called biphasic anaphylaxis).[31] All people who have experienced or are at risk for anaphylaxis should have access to self-injectable epinephrine at all times.[6]
Epinephrine is the first medication used to treat anaphylaxis. When administered promptly, it is lifesaving. Epinephrine (also known as adrenaline) increases blood pressure by constricting blood vessels (thereby preventing cardiovascular collapse), prevents or decreases swelling of the airways and promotes dilation of the airways (allowing air to better flow to and from the lungs), decreases the activity of mast cells and basophils (both of which release mediators that cause inflammation), and helps the heart beat more effectively (promoting blood flow).[32] Adverse effects include anxiety, restlessness, palpitations, headache, dizziness, pallor, and tremor.[33] Serious adverse effects, like dangerous heart arrhythmias, are rare.[34]
Although epinephrine rapidly treats most of the dangerous symptoms of anaphylaxis, it is not a “cure” for allergic reactions or a replacement for immediately seeking medical help. Instead, epinephrine auto-injectors are a way to prevent serious complications from occurring before being seen by a clinician for additional evaluation and care. In some cases, additional medications may be needed to fully treat someone’s symptoms, or the allergic symptoms may return even after they initially resolved. Thus, medical monitoring is important after using auto-injectors.
A history of consistent allergic signs and symptoms after the ingestion of a tree nut is the first step in diagnosing a tree nut allergy. An allergist will use this history in conjunction with a physical exam to guide the choice of additional diagnostic tests.
The skin prick test is the most common diagnostic test and involves introducing the allergen into the skin through a small prick with a special tool. If IgE antibodies to tree nuts are present, the area that was pricked will swell. A swollen area 3 mm or greater in size is usually considered positive for an allergy, although some clinicians prefer an 8 mm or greater standard to decrease the chance of a false positive.[4] Blood tests that detect food-specific IgE antibodies may also be used to aid in the diagnosis.
Although these diagnostic tests are helpful, they do not predict the severity of a person’s allergic reaction, nor are they useful in people without a history of allergic signs and symptoms (given the frequency of false positives). In some cases, an oral food challenge, which consists of gradual consumption of the allergen under direct medical supervision, may be recommended to confirm the allergy.[5][6] Ideally, allergy testing is done yearly because some allergies change or resolve over time.
Certain people are more likely to develop a tree nut allergy, like people who are allergic to other foods or people who have atopic dermatitis (eczema).[21][22][23] Other risk factors include age (food allergies are more common in children), a family history of allergy or atopy, certain genetic mutations, non-Hispanic black or Asian ethnicity, male sex, certain environmental factors (e.g., limited microbial exposure in infancy) and occupational exposures, and delayed introduction of allergenic foods.[24] However, there is conflicting or insufficient evidence on some of the risk factors for food allergies, such as vitamin D deficiency, use of antacids, duration of breastfeeding in infancy, and low intake of omega-3 fatty acids.[25]
Having a tree nut allergy may also increase the risk of developing other health conditions. In particular, children with IgE-mediated food allergies are more likely than nonallergic children to be diagnosed with allergic rhinitis and asthma.[26][27]
Sensitization is different from an allergy. Sensitization means that the immune system is producing food-specific antibodies, but sensitization alone is not diagnostic for an allergy. In fact, people can be sensitized to foods, like tree nuts, without experiencing any symptoms upon exposure.[36] This is why a history of consistent allergic signs and symptoms after exposure to a food is a necessary component of a food allergy diagnosis.
Food intolerances are separate from food allergies and do not involve the immune system. An intolerance to a food means that a person is unable to properly digest the food, causing gastrointestinal symptoms (like bloating, nausea, and cramps).
Avoiding exposure to tree nuts is the first line of treatment for a tree nut allergy. This includes not eating foods that may be contaminated with tree nuts.[5]
When exposure does occur, medications can be used to treat allergic signs and symptoms. If the reaction is mild, antihistamines may be helpful, but severe reactions should be treated with epinephrine.[7] Prompt treatment is critical in preventing life-threatening reactions. For this reason, most people with a tree nut allergy are prescribed an epinephrine auto-injector and are instructed to carry it with them at all times in case of an emergency.
Not all tree nut allergies can be prevented, but certain factors are associated with a lower risk of developing a tree nut allergy. These factors include early exposure to tree nuts (usually beginning around the age of 4 to 6 months), adequate vitamin D levels (vitamin D is implicated in the regulation of immune cells), early exposure to microorganisms and infections (known as the “hygiene hypothesis”), and maintaining the skin barrier (i.e., avoiding dry/cracked skin). Colloquially, these contributing factors are summarized as the “5Ds” for diet, vitamin D, dogs, dirt or dribble, and dry skin.[20]
Vitamin D supplementation is an area of ongoing research for the prevention of food allergies. Vitamin D is integral to the proper functioning of the immune system, and vitamin D insufficiency and limited sun exposure are associated with the development of food allergies in observational research.[8][9][10][11] However, whether vitamin D supplementation actually decreases the incidence of food allergies is not clear.[12]
Currently, there is also no evidence to support the use of supplements in treating tree nut allergies. However, there is ongoing research investigating the effects of certain Chinese herbs on the immune system, including their potential to dampen the inappropriate immunologic response to food proteins.[13] Of these herbs, berberine appears to be the most powerful suppressor of IgE production.[14] More research is needed to determine whether these supplements could decrease allergic reactions.
Diet is the cornerstone of tree nut allergy management. People with tree nut allergies need to carefully plan their diets to avoid eating certain tree nuts. This means also avoiding foods that contain or may be contaminated with tree nuts, such as food products made in facilities that use nuts in other products, which is a potential source of cross-contamination. Most countries require that food labels clearly state whether a food contains tree nuts, and many labels voluntarily state whether cross-contamination is possible, so checking the label on all packaged food items is important for people with allergies.
Diet may even play a role in allergy prevention. Early introduction of allergenic foods (by approximately 6 months of age) alongside continued consumption reduces the risk of developing food allergies.[15][16][17]
Many people with an allergy to one tree nut have allergies to other tree nuts or foods, which can further complicate dietary choices. For example, people who are allergic to cashews are often also allergic to pistachios because they are both part of the Anarcadiaceae family and can have the same or similar IgE binding proteins.[37] This latter case is called cross-reactivity, and it can also occur with walnuts and pecans and with almonds and hazelnuts. Peanuts and eggs are other potential allergens among people with tree nut allergies.[38]
Allergen avoidance and medications for accidental exposure are the mainstays of tree nut allergy management. Other treatments, such as immunotherapy and monoclonal anti-IgE antibodies, are under investigation for their efficacy in treating food allergies, including tree nut allergy. The main goal of these immune-modulating therapies is to allow a person with a food allergy to be exposed to their allergen without experiencing a severe reaction.[18][19]
Tree nut allergies are usually lifelong, but a type of treatment called immunotherapy may desensitize a person or even induce permanent tolerance to an allergen, which allows the person to eat their allergen without a reaction. Immunotherapy involves exposing the allergic person to small amounts of the allergen in a medically supervised setting and gradually increasing the exposure dose over several months until the person reaches and no longer reacts to their “maintenance dose” (which is an individualized goal).
The allergen is usually introduced through the mouth (e.g., oral immunotherapy, sublingual immunotherapy), but it can also be introduced through the skin (e.g., epicutaneous immunotherapy, subcutaneous immunotherapy). Currently, oral immunotherapy is available for peanuts, but research on immunotherapy specific to tree nuts is ongoing.[35]
Tree nut allergies are caused by an inappropriate reaction of the immune system to the proteins found in tree nuts. Normally, the immune system targets and attacks pathogens like viruses and bacteria but in the case of food allergies, the immune system identifies a certain food as an “invader” and launches an immune response against it.
This breakdown of immune tolerance is primarily driven by T helper 2 cells and often includes the production of food-specific IgE antibodies, all of which lead to a cascade of immune responses (like the activation of mast cells and release of cytokines) that cause allergic symptoms. Why the immune system reacts abnormally to certain foods in some people is not fully understood.[20]