Allergy-Immunology Glossary

Food allergy

A food allergy is an adverse immune response to a food protein.[1][2] Food allergy is distinct from other adverse responses to food, such as food intolerance, pharmacologic reactions, and toxin-mediated reactions.

Food Allergy: adverse immune response to a food protein
Pharmacologic: caffeine tremors, cheese/wine (tyramine) migraine, scombroid (histamine) fish poisoning
Toxins: bacterial food poisoning, staphylotoxin
Intolerance: lactose intolerance (lactase deficiency)

The food protein triggering the allergic response is termed a food allergen. It is estimated that up to 12 million Americans have food allergies,[3] and the prevalence is rising.[4] Six to eight percent of children under the age of three have food allergies and nearly four percent of adults have them.[5] Food allergies cause roughly 30,000 emergency room visits and 100 to 200 deaths per year in the United States.[6] The most common food allergies in adults are shellfish, peanuts, tree nuts, fish, and eggs,[5] and the most common food allergies in children are milk, eggs, peanuts, and tree nuts.[5]

Treatment consists of avoidance diets, in which the allergic person avoids all forms of the food to which they are allergic. For people who are extremely sensitive, this may involve the total avoidance of any exposure with the allergen, including touching or inhaling the problematic food as well as touching any surfaces that may have come into contact with it. Areas of research include anti-IgE antibody (omalizumab, or Xolair) and specific oral tolerance induction (SOTI), which have shown some promise for treatment of certain food allergies. People diagnosed with a food allergy may carry an autoinjector of epinephrine such as an EpiPen or Twinject, wear some form of medical alert jewelry, or develop an emergency action plan, in accordance with their doctor.

Signs and symptoms:

Classic immunoglobulin-E (IgE)-mediated food allergies are classified as type-I immediate hypersensitivity reactions. These allergic reactions have an acute onset (from seconds to one hour) and may include:[7]

Angioedema: soft tissue swelling, usually involving the eyelids, face, lips, and tongue. Angioedema may result in severe swelling of the tongue as well as the larynx (voice box) and trachea, resulting in upper airway obstruction and difficulty breathing.
Hives
Itching of the mouth, throat, eyes, skin
Nausea, vomiting, diarrhea, stomach cramps, and/or abdominal pain. This group of symptoms is termed gastrointestinal hypersensitivity.
Rhinorrhea, nasal congestion
Wheezing, scratchy throat, shortness of breath, or difficulty swallowing
Anaphylaxis: a severe, whole-body allergic reaction that can result in death (see below)

The reaction may progress to anaphylactic shock: A systemic reaction involving several different bodily systems including hypotension (low blood pressure),loss of consciousness, and possibly death. Allergens most frequently associated with this type of reaction are peanuts, nuts, milk, egg, and seafood, though many food allergens have been reported as triggers for anaphylaxis.

Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma.[8] The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.

Conditions caused by food allergies are classified into 3 groups according to the mechanism of the allergic response:
1. IgE-mediated (classic):

Type-I immediate hypersensitivity reaction (symptoms described above)
Oral allergy syndrome

2. IgE and/or non-IgE-mediated:

Allergic eosinophilic esophagitis
Allergic eosinophilic gastritis
Allergic eosinophilic gastroenteritis

3. Non-IgE mediated:

Food protein-induced Enterocolitis syndrome (FPIES)
Food protein proctocolitis/proctitis
Food protein-induced enteropathy. An important example is Coeliac disease, which is an adverse immune response to the protein gluten.
Milk-soy protein intolerance (MSPI) is a non-medical term used to describe a non-IgE mediated allergic response to milk and/or soy protein during infancy and early childhood. Symptoms of MSPI are usually attributable to food protein proctocolitis or FPIES.
Heiner syndrome - lung disease due to formation of milk protein/IgG antibody immune complexes (milk precipitins) in the blood stream after it is absorbed from the GI tract. The lung disease commonly causes bleeding into the lungs and results in pulmonary hemosiderosis.

The big eight
The most common food allergies are:[9]

Dairy allergy
Egg allergy
Peanut allergy
Tree nut allergy
Seafood allergy
Shellfish allergy
Soy allergy
Wheat allergy

These are often referred to as "the big eight."[10] They account for over 90% of the food allergies in the United States.[11]

The top allergens vary somewhat from country to country but milk, eggs, peanuts, treenuts, fish, shellfish, soy, wheat and sesame tend to be in the top 10 in many countries.[citation needed] Allergies to seeds - especially sesame - seem to be increasing in many countries.[12]

More rare food allergies:
Likelihood of allergy can increase with exposure[citation needed]. For example, rice allergy is more common in East Asia where rice forms a large part of the diet.[13]
In Central Europe, celery allergy is more common. In Japan, allergy to buckwheat flour, used for Soba noodles, is more common.
Red meat allergy is extremely rare in the general population, but a geographic cluster of people allergic to red meat has been observed in Sydney, Australia.[14] There appears to be a possible association between localised reaction to tick bite and the development of red meat allergy.
Fruit allergies exist, such as to apples, pears, jackfruit, strawberries, etc.
Corn allergy may also be prevalent in many populations, although it may be difficult to recognize in areas such as the United States and Canada where corn derivatives are common in the food supply.[15]

Diagnosis:
The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will review the patient's history and the symptoms or reactions that have been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will perform allergy tests.

Examples of allergy testing include:

Skin prick testing is easy to do and results are available in minutes. Different allergists may use different devices for skin prick testing. Some use a "bifurcated needle", which looks like a fork with 2 prongs. Others use a "multi-test", which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular food or not, because it detects allergic antibodies known as IgE. Skin tests cannot predict if a reaction would occur or what kind of reaction might occur if a person ingests that particular allergen. They can however confirm an allergy in light of a patient's history of reactions to a particular food. Non-IgE mediated allergies cannot be detected by this method.
Blood tests are another useful diagnostic tool for evaluating IgE-mediated food allergies. For example, the RAST (RadioAllergoSorbent Test)detects the presence of IgE antibodies to a particular allergen. A CAP-RAST test is a specific type of RAST test with greater specificity: it can show the amount of IgE present to each allergen.[16] Researchers have been able to determine "predictive values" for certain foods. These predictive values can be compared to the RAST blood test results. If a persons RAST score is higher than the predictive value for that food, then there is over a 95% chance the person will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food.[citation needed] Currently, predictive values are available for the following foods: milk, egg, peanut, fish, soy, and wheat.[17][18][19] Blood tests allow for hundreds of allergens to be screened from a single sample, and cover food allergies as well as inhalants. However, non-IgE mediated allergies cannot be detected by this method.
Food challenges, especially double-blind placebo-controlled food challenges (DBPCFC), are the gold standard for diagnosis of food allergies, including most non-IgE mediated reactions. Blind food challenges involve packaging the suspected allergen into a capsule, giving it to the patient, and observing the patient for signs or symptoms of an allergic reaction. Due to the risk of anaphylaxis, food challenges are usually conducted in a hospital environment in the presence of a doctor.
Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy.

Important differential diagnoses are:

Lactose intolerance; this generally develops later in life but can present in young patients in severe cases. This is due to an enzyme deficiency (lactase) and not allergy. It occurs in many non-Western people.
Celiac disease; this is an autoimmune disorder triggered by gluten proteins such as gliadin (present in wheat, rye and barley). It is a non-IgE mediated food allergy by definition.
Irritable bowel syndrome (IBS)
C1 esterase inhibitor deficiency (hereditary angioedema); this rare disease generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea.

Causes:
The immune system's eosinophils, once activated in a histamine reaction, will register any foreign proteins they see. One theory regarding the causes of food allergies focuses on proteins presented in the blood along with vaccines, which are designed to provoke an immune response. Influenza vaccines and the Yellow Fever vaccine are still egg-based, but the Measles-Mumps-Rubella vaccine stopped using eggs in 1994.[20] However large scientific studies do not support this theory, especially as it applies to autoimmune disease.[21]

Another theory focuses on whether an infant's immune system is ready for complex proteins in a new food when it is first introduced.[22]

One hypothesis at this time is the Hygiene hypothesis. While there is no proof for the hygiene hypothesis, people speculate[citation needed] that in modern, industrialized nations, such as the United States, food allergies are more common due to the lack of early exposure to dirt and germs, in part due to the over-use of antibiotics and antibiotic cleansers. This hypothesis is based partly on studies showing less allergy in third world countries.[citation needed] Some research suggests[citation needed] that the body, with less dirt and germs to fight off, turns on itself and attacks food proteins as if they were foreign invaders.

Antibiotics have also been implicated in Leaky Gut Syndrome which is another possible cause of food allergies[citation needed].

A lower incidence of food allergies in the developing world could also be due to differences in diet from the West and less exposure to food allergens.

Others have found that food allergies are due to widespread usage of baby skin-care products that contain allergens, such as lotions based upon peanut oil. These skin-care products are cheaper to manufacture than non-allergenic ones and using them sensitizes the baby, which later develops into a food allergy. This theory has yet to come with sufficient explanation as to why the occurrence of allergies has been on a steady rise in the last two decades.

Prevention
According to a report issued by the American Academy of Pediatrics, "There is evidence that breastfeeding for at least 4 months, compared with feeding infants formula made with intact cow milk protein, prevents or delays the occurrence of atopic dermatitis, cow milk allergy, and wheezing in early childhood."[23]

Treatment:
The mainstay of treatment for food allergy is avoidance of the foods that have been identified as allergens.

If the food is accidentally ingested and a systemic reaction (anaphylaxis) occurs, then epinephrine (best delivered with an autoinjector of epinephrine such as an Epipen or Twinject) should be used. It is possible that a second dose of epinephrine may be required for severe reactions.[citation needed] The patient should also seek medical care immediately.

At this time, there is no cure for food allergies.[24] There are no allergy desensitization or allergy "shots" available for food allergies.[citation needed] Some doctors feel they do not work in food allergies because even minute amounts of the food in question or even food extracts (as in the case of allergy shots) can cause an allergic response in many sufferers.

Ronald van Ree of Amsterdam University expects that vaccines can in theory be created using genetic engineering to cure allergies. If this can be done, food allergies could be eradicated in about ten years.[25]

Allergy-Immunology Glossary
Heart Murmur Adenoids Bursitis Eye Infections Hepatitis C Glomerulonephritis (GN) Male And Female Infertility - Causes Escherichia Coli O157 Clostridium Epstein-Barr virus Cervical cancer Allergy-Immunology Glossary Mumps Cancer Head And Neck Blood Coagulation Disorders Sickle-Cell Disease Gastrointestinal Disorders Common cold Warts - Causes, Symptoms, And Treatment What Causes Acne Clarithromycin Leishmania Infection Angiostrongylus Infection Tuberculosis Addison's disease Coming Soon Headaches And Allergies Hay fever Hand, Foot, & Mouth Disease Pubic Lice Infestation Psoriasis Protein Suppresses Allergy Prostate Cancer Prenatal Testing Prader-Willi Syndrome Post-Traumatic Stress Disorder (PTSD) Poison Plants Pneumococcal Disease Plague Pet Allergy Penicillin Allergy Patent Ductus Arteriosus (PDA) Polio Disease Pinworm Infection Pheochromocytoma Phenylketonuria Pertussis Disease PAD (Peripheral Arterial Disease) Peanut Allergy Symptoms Parvovirus B19 (Fifth Disease) Pacemaker	Food allergy A food allergy is an adverse immune response to a food protein.[1][2] Food allergy is distinct from other adverse responses to food, such as food intolerance, pharmacologic reactions, and toxin-mediated reactions. Food Allergy: adverse immune response to a food protein Pharmacologic: caffeine tremors, cheese/wine (tyramine) migraine, scombroid (histamine) fish poisoning Toxins: bacterial food poisoning, staphylotoxin Intolerance: lactose intolerance (lactase deficiency) The food protein triggering the allergic response is termed a food allergen. It is estimated that up to 12 million Americans have food allergies,[3] and the prevalence is rising.[4] Six to eight percent of children under the age of three have food allergies and nearly four percent of adults have them.[5] Food allergies cause roughly 30,000 emergency room visits and 100 to 200 deaths per year in the United States.[6] The most common food allergies in adults are shellfish, peanuts, tree nuts, fish, and eggs,[5] and the most common food allergies in children are milk, eggs, peanuts, and tree nuts.[5] Treatment consists of avoidance diets, in which the allergic person avoids all forms of the food to which they are allergic. For people who are extremely sensitive, this may involve the total avoidance of any exposure with the allergen, including touching or inhaling the problematic food as well as touching any surfaces that may have come into contact with it. Areas of research include anti-IgE antibody (omalizumab, or Xolair) and specific oral tolerance induction (SOTI), which have shown some promise for treatment of certain food allergies. People diagnosed with a food allergy may carry an autoinjector of epinephrine such as an EpiPen or Twinject, wear some form of medical alert jewelry, or develop an emergency action plan, in accordance with their doctor. Signs and symptoms: Classic immunoglobulin-E (IgE)-mediated food allergies are classified as type-I immediate hypersensitivity reactions. These allergic reactions have an acute onset (from seconds to one hour) and may include:[7] Angioedema: soft tissue swelling, usually involving the eyelids, face, lips, and tongue. Angioedema may result in severe swelling of the tongue as well as the larynx (voice box) and trachea, resulting in upper airway obstruction and difficulty breathing. Hives Itching of the mouth, throat, eyes, skin Nausea, vomiting, diarrhea, stomach cramps, and/or abdominal pain. This group of symptoms is termed gastrointestinal hypersensitivity. Rhinorrhea, nasal congestion Wheezing, scratchy throat, shortness of breath, or difficulty swallowing Anaphylaxis: a severe, whole-body allergic reaction that can result in death (see below) The reaction may progress to anaphylactic shock: A systemic reaction involving several different bodily systems including hypotension (low blood pressure),loss of consciousness, and possibly death. Allergens most frequently associated with this type of reaction are peanuts, nuts, milk, egg, and seafood, though many food allergens have been reported as triggers for anaphylaxis. Food allergy is thought to develop more easily in patients with the atopic syndrome, a very common combination of diseases: allergic rhinitis and conjunctivitis, eczema and asthma.[8] The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome. Conditions caused by food allergies are classified into 3 groups according to the mechanism of the allergic response: 1. IgE-mediated (classic): Type-I immediate hypersensitivity reaction (symptoms described above) Oral allergy syndrome 2. IgE and/or non-IgE-mediated: Allergic eosinophilic esophagitis Allergic eosinophilic gastritis Allergic eosinophilic gastroenteritis 3. Non-IgE mediated: Food protein-induced Enterocolitis syndrome (FPIES) Food protein proctocolitis/proctitis Food protein-induced enteropathy. An important example is Coeliac disease, which is an adverse immune response to the protein gluten. Milk-soy protein intolerance (MSPI) is a non-medical term used to describe a non-IgE mediated allergic response to milk and/or soy protein during infancy and early childhood. Symptoms of MSPI are usually attributable to food protein proctocolitis or FPIES. Heiner syndrome - lung disease due to formation of milk protein/IgG antibody immune complexes (milk precipitins) in the blood stream after it is absorbed from the GI tract. The lung disease commonly causes bleeding into the lungs and results in pulmonary hemosiderosis. The big eight The most common food allergies are:[9] Dairy allergy Egg allergy Peanut allergy Tree nut allergy Seafood allergy Shellfish allergy Soy allergy Wheat allergy These are often referred to as "the big eight."[10] They account for over 90% of the food allergies in the United States.[11] The top allergens vary somewhat from country to country but milk, eggs, peanuts, treenuts, fish, shellfish, soy, wheat and sesame tend to be in the top 10 in many countries.[citation needed] Allergies to seeds - especially sesame - seem to be increasing in many countries.[12] More rare food allergies: Likelihood of allergy can increase with exposure[citation needed]. For example, rice allergy is more common in East Asia where rice forms a large part of the diet.[13] In Central Europe, celery allergy is more common. In Japan, allergy to buckwheat flour, used for Soba noodles, is more common. Red meat allergy is extremely rare in the general population, but a geographic cluster of people allergic to red meat has been observed in Sydney, Australia.[14] There appears to be a possible association between localised reaction to tick bite and the development of red meat allergy. Fruit allergies exist, such as to apples, pears, jackfruit, strawberries, etc. Corn allergy may also be prevalent in many populations, although it may be difficult to recognize in areas such as the United States and Canada where corn derivatives are common in the food supply.[15] Diagnosis: The best method for diagnosing food allergy is to be assessed by an allergist. The allergist will review the patient's history and the symptoms or reactions that have been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will perform allergy tests. Examples of allergy testing include: Skin prick testing is easy to do and results are available in minutes. Different allergists may use different devices for skin prick testing. Some use a "bifurcated needle", which looks like a fork with 2 prongs. Others use a "multi-test", which may look like a small board with several pins sticking out of it. In these tests, a tiny amount of the suspected allergen is put onto the skin or into a testing device, and the device is placed on the skin to prick, or break through, the top layer of skin. This puts a small amount of the allergen under the skin. A hive will form at any spot where the person is allergic. This test generally yields a positive or negative result. It is good for quickly learning if a person is allergic to a particular food or not, because it detects allergic antibodies known as IgE. Skin tests cannot predict if a reaction would occur or what kind of reaction might occur if a person ingests that particular allergen. They can however confirm an allergy in light of a patient's history of reactions to a particular food. Non-IgE mediated allergies cannot be detected by this method. Blood tests are another useful diagnostic tool for evaluating IgE-mediated food allergies. For example, the RAST (RadioAllergoSorbent Test)detects the presence of IgE antibodies to a particular allergen. A CAP-RAST test is a specific type of RAST test with greater specificity: it can show the amount of IgE present to each allergen.[16] Researchers have been able to determine "predictive values" for certain foods. These predictive values can be compared to the RAST blood test results. If a persons RAST score is higher than the predictive value for that food, then there is over a 95% chance the person will have an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food.[citation needed] Currently, predictive values are available for the following foods: milk, egg, peanut, fish, soy, and wheat.[17][18][19] Blood tests allow for hundreds of allergens to be screened from a single sample, and cover food allergies as well as inhalants. However, non-IgE mediated allergies cannot be detected by this method. Food challenges, especially double-blind placebo-controlled food challenges (DBPCFC), are the gold standard for diagnosis of food allergies, including most non-IgE mediated reactions. Blind food challenges involve packaging the suspected allergen into a capsule, giving it to the patient, and observing the patient for signs or symptoms of an allergic reaction. Due to the risk of anaphylaxis, food challenges are usually conducted in a hospital environment in the presence of a doctor. Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy. Important differential diagnoses are: Lactose intolerance; this generally develops later in life but can present in young patients in severe cases. This is due to an enzyme deficiency (lactase) and not allergy. It occurs in many non-Western people. Celiac disease; this is an autoimmune disorder triggered by gluten proteins such as gliadin (present in wheat, rye and barley). It is a non-IgE mediated food allergy by definition. Irritable bowel syndrome (IBS) C1 esterase inhibitor deficiency (hereditary angioedema); this rare disease generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea. Causes: The immune system's eosinophils, once activated in a histamine reaction, will register any foreign proteins they see. One theory regarding the causes of food allergies focuses on proteins presented in the blood along with vaccines, which are designed to provoke an immune response. Influenza vaccines and the Yellow Fever vaccine are still egg-based, but the Measles-Mumps-Rubella vaccine stopped using eggs in 1994.[20] However large scientific studies do not support this theory, especially as it applies to autoimmune disease.[21] Another theory focuses on whether an infant's immune system is ready for complex proteins in a new food when it is first introduced.[22] One hypothesis at this time is the Hygiene hypothesis. While there is no proof for the hygiene hypothesis, people speculate[citation needed] that in modern, industrialized nations, such as the United States, food allergies are more common due to the lack of early exposure to dirt and germs, in part due to the over-use of antibiotics and antibiotic cleansers. This hypothesis is based partly on studies showing less allergy in third world countries.[citation needed] Some research suggests[citation needed] that the body, with less dirt and germs to fight off, turns on itself and attacks food proteins as if they were foreign invaders. Antibiotics have also been implicated in Leaky Gut Syndrome which is another possible cause of food allergies[citation needed]. A lower incidence of food allergies in the developing world could also be due to differences in diet from the West and less exposure to food allergens. Others have found that food allergies are due to widespread usage of baby skin-care products that contain allergens, such as lotions based upon peanut oil. These skin-care products are cheaper to manufacture than non-allergenic ones and using them sensitizes the baby, which later develops into a food allergy. This theory has yet to come with sufficient explanation as to why the occurrence of allergies has been on a steady rise in the last two decades. Prevention According to a report issued by the American Academy of Pediatrics, "There is evidence that breastfeeding for at least 4 months, compared with feeding infants formula made with intact cow milk protein, prevents or delays the occurrence of atopic dermatitis, cow milk allergy, and wheezing in early childhood."[23] Treatment: The mainstay of treatment for food allergy is avoidance of the foods that have been identified as allergens. If the food is accidentally ingested and a systemic reaction (anaphylaxis) occurs, then epinephrine (best delivered with an autoinjector of epinephrine such as an Epipen or Twinject) should be used. It is possible that a second dose of epinephrine may be required for severe reactions.[citation needed] The patient should also seek medical care immediately. At this time, there is no cure for food allergies.[24] There are no allergy desensitization or allergy "shots" available for food allergies.[citation needed] Some doctors feel they do not work in food allergies because even minute amounts of the food in question or even food extracts (as in the case of allergy shots) can cause an allergic response in many sufferers. Ronald van Ree of Amsterdam University expects that vaccines can in theory be created using genetic engineering to cure allergies. If this can be done, food allergies could be eradicated in about ten years.[25]
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