What does class 2 food allergy mean

The mainstay of treatment for food allergy is entire avoidance of the foods identified as allergens. An allergen can enter the body by consuming a food containing the allergen, and can also be ingested by touching any surfaces that may own come into contact with the allergen, then touching the eyes or nose. For people who are extremely sensitive, avoidance includes avoiding touching or inhaling the problematic food. Entire avoidance is complicated because the declaration of the presence of trace amounts of allergens in foods is not mandatory (see regulation of labelling).

If the food is accidentally ingested and a systemic reaction (anaphylaxis) occurs, then epinephrine should be used. A second dose of epinephrine may be required for severe reactions. The person should then be transported to the emergency room, where additional treatment can be given. Other treatments include antihistamines and steroids.[65]

Antihistamines

Antihistamines can alleviate some of the milder symptoms of an allergic reaction, but do not treat every symptoms of anaphylaxis.[67] Antihistamines block the action of histamine, which causes blood vessels to dilate and become leaky to plasma proteins.

Histamine also causes itchiness by acting on sensory nerve terminals. The most common antihistamine given for food allergies is diphenhydramine.

What does class 2 food allergy mean

Epinephrine

Epinephrine (adrenaline) is the first-line treatment for severe allergic reactions (anaphylaxis). If istered in a timely manner, epinephrine can reverse its effects. Epinephrine relieves airway swelling and obstruction, and improves blood circulation; blood vessels are tightened and heart rate is increased, improving circulation to body organs. Epinephrine is available by prescription in an autoinjector.[66]

Steroids

Glucocorticoid steroids are used to calm below the immune system cells that are attacked by the chemicals released during an allergic reaction.

This treatment in the form of a nasal spray should not be used to treat anaphylaxis, for it only relieves symptoms in the area in which the steroid is in contact. Another reason steroids should not be used is the delay in reducing inflammation.

What does class 2 food allergy mean

Steroids can also be taken orally or through injection, by which every part of the body can be reached and treated, but a endless time is generally needed for these to take effect.[68]


Epidemiology

The most common food allergens account for about 90% of every allergic reactions;[69] in adults they include shellfish, peanuts, tree nuts, fish, and egg.[70] In children, they include milk, eggs, peanuts, and tree nuts.[70] Six to 8% of children under the age of three own food allergies and almost 4% of adults own food allergies.[70][better source needed][clarification needed]

For reasons not entirely understood, the diagnosis of food allergies has apparently become more common in Western nations recently.[71] One possible explanation for this is the «old friends» hypothesis which suggests that non disease causing organisms, such as helminths, could protect against allergy.

Therefore, reduced exposure to these organisms, particularly in developed countries, could own contributed towards the increase.[72]

In the United States, food allergy affects as numerous as 5% of infants less than three years of age[73] and 3% to 4% of adults.[74] A similar prevalence is found in Canada.[75]

About 75% of children who own allergies to milk protein are capable to tolerate baked-in milk products, i.e., muffins, cookies, cake, and hydrolyzed formulas.[76]

About 50% of children with allergies to milk, egg, soy, peanuts, tree nuts, and wheat will outgrow their allergy by the age of 6.

Those who are still allergic by the age of 12 or so own less than an 8% chance of outgrowing the allergy.[77]

Peanut and tree nut allergies are less likely to be outgrown, although evidence now[when?] shows[78] that about 20% of those with peanut allergies and 9% of those with tree nut allergies will outgrow them.[79]

In Japan, allergy to buckwheat flour, used for soba noodles, is more common than peanuts, tree nuts or foods made from soy beans.[80]

United States

In the United States, an estimated 12 million people own food allergies. Food allergy affects as numerous as 5% of infants less than three years of age[73] and 3% to 4% of adults.[74][81] The prevalence of food allergies is rising.[71][82][83] Food allergies cause roughly 30,000 emergency room visits and 150 deaths per year.[84]


Signs and symptoms

Food allergies generally own a quick onset (from seconds to one hour) and may include:[13]

  1. Fainting[13]
  2. Swelling (angioedema) of lips, tongue, eyelids, or the whole face[13]
  3. Diarrhea, abdominal pain, and/or stomach cramps[13]
  4. Rash
  5. Lightheadedness[13]
  6. Itching of mouth, lips, tongue, throat, eyes, skin, or other areas[13]
  7. Runny or congested nose[13]
  8. Hoarse voice[13]
  9. Nausea[13]
  10. Hives[13]
  11. Difficulty swallowing[13]
  12. Wheezing and/or shortness of breath[13]
  13. Vomiting[13]

In some cases, however, onset of symptoms may be delayed for hours.[13]

Symptoms can vary.

The quantity of food needed to trigger a reaction also varies.[14]

Serious harm regarding allergies can start when the respiratory tract or blood circulation is affected. The previous can be indicated through wheezing and cyanosis. Poor blood circulation leads to a feeble pulse, pale skin and fainting.[15]

A severe case of an allergic reaction, caused by symptoms affecting the respiratory tract and blood circulation, is called anaphylaxis.

What does class 2 food allergy mean

When symptoms are related to a drop in blood pressure, the person is said to be in anaphylactic shock. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show symptoms.[16] Those with asthma or an allergy to peanuts, tree nuts, or seafood are at greater risk for anaphylaxis.[17]


Prevention

Breastfeeding for more than four months may prevent atopic dermatitis, cow’s milk allergy, and wheezing in early childhood.[58] Early exposure to potential allergens may be protective.[2] Specifically, early exposure to eggs and peanuts reduces the risk of allergies to these.[3] Guidelines propose introducing peanuts as early as 4–6 months and include precautionary measures for high-risk infants.[59] The previous guidelines, advising delaying the introduction of peanuts, are now[when?] thought to own contributed to the increase in peanut allergy seen recently.[60][better source needed]

To avoid an allergic reaction, a strict diet can be followed.

It is hard to determine the quantity of allergenic food required to elicit a reaction, so finish avoidance should be attempted. In some cases, hypersensitive reactions can be triggered by exposures to allergens through skin contact, inhalation, kissing, participation in sports, blood transfusions, cosmetics, and alcohol.[61]

Inhalation exposure

Allergic reactions to airborne particles or vapors of known food allergens own been reported as an occupational consequence of people working in the food industry, but can also take put in home situations, restaurants, or confined spaces such as airplanes.

According to two reviews, respiratory symptoms are common, but in some cases there has been progression to anaphylaxis.[62][63] The most frequent reported cases of reactions by inhalation of allergenic foods were due to peanut, seafood, legumes, tree nut, and cow’s milk.[62] Steam rising from cooking of lentils, green beans, chickpeas and fish has been well documented as triggering reactions, including anaphylactic reactions.[62][64] One review mentioned case study examples of allergic responses to inhalation of other foods, including examples in which oral consumption of the food is tolerated.[62]


Pathophysiology

Conditions caused by food allergies are classified into three groups according to the mechanism of the allergic response:[36]

  • Non-IgE mediated – characterized by an immune response not involving immunoglobulin E; may happen some hours after eating, complicating diagnosis
  • IgE-mediated (classic) – the most common type, occurs shortly after eating and may involve anaphylaxis.
  • IgE and/or non-IgE-mediated – a hybrid of the above two types

Allergic reactions are hyperactive responses of the immune system to generally innocuous substances.

When immune cells encounter the allergenic protein, IgE antibodies are produced; this is similar to the immune system’s reaction to foreign pathogens. The IgE antibodies identify the allergenic proteins as harmful and initiate the allergic reaction. The harmful proteins are those that do not break below due to the strong bonds of the protein. IgE antibodies bind to a receptor on the surface of the protein, creating a tag, just as a virus or parasite becomes tagged. Why some proteins do not denature and subsequently trigger allergic reactions and hypersensitivity while others do is not entirely clear.[37]

Hypersensitivities are categorized according to the parts of the immune system that are attacked and the quantity of time it takes for the response to happen.

The four types of hypersensitivity reaction are: type 1, immediate IgE-mediated; type 2, cytotoxic; type 3, immune complex-mediated; and type 4, delayed cell-mediated.[38] The pathophysiology of allergic responses can be divided into two phases. The first is an acute response that occurs immediately after exposure to an allergen. This phase can either subside or progress into a «late-phase reaction» which can substantially prolong the symptoms of a response, and result in tissue damage.

Many food allergies are caused by hypersensitivities to specific proteins in diverse foods.

Proteins own unique properties that permit them to become allergens, such as stabilizing forces in their tertiary and quaternary structures which prevent degradation during digestion. Numerous theoretically allergenic proteins cannot survive the destructive environment of the digestive tract, thus do not trigger hypersensitive reactions.[39]

Acute response

In the early stages of allergy, a type I hypersensitivity reaction against an allergen, encountered for the first time, causes a response in a type of immune cell called a TH2 lymphocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 (IL-4).

These TH2 cells interact with other lymphocytes called B cells, whose role is the production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to start production of a large quantity of a specific type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a helpful of Fc receptor called FcεRI) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen.[40]

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils.

Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complicated interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth-muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis. Depending on the individual, the allergen, and the mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to specific body systems.[40]

Late-phase response

After the chemical mediators of the acute response subside, late-phase responses can often happen due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils, and macrophages to the initial site.

The reaction is generally seen 2–24 hours after the original reaction.[41] Cytokines from mast cells may also frolic a role in the persistence of long-term effects.[42]

Allergic reactions are hyperactive responses of the immune system to generally innocuous substances. When immune cells encounter the allergenic protein, IgE antibodies are produced; this is similar to the immune system’s reaction to foreign pathogens. The IgE antibodies identify the allergenic proteins as harmful and initiate the allergic reaction.

The harmful proteins are those that do not break below due to the strong bonds of the protein. IgE antibodies bind to a receptor on the surface of the protein, creating a tag, just as a virus or parasite becomes tagged. Why some proteins do not denature and subsequently trigger allergic reactions and hypersensitivity while others do is not entirely clear.[37]

Hypersensitivities are categorized according to the parts of the immune system that are attacked and the quantity of time it takes for the response to happen. The four types of hypersensitivity reaction are: type 1, immediate IgE-mediated; type 2, cytotoxic; type 3, immune complex-mediated; and type 4, delayed cell-mediated.[38] The pathophysiology of allergic responses can be divided into two phases.

The first is an acute response that occurs immediately after exposure to an allergen. This phase can either subside or progress into a «late-phase reaction» which can substantially prolong the symptoms of a response, and result in tissue damage.

Many food allergies are caused by hypersensitivities to specific proteins in diverse foods. Proteins own unique properties that permit them to become allergens, such as stabilizing forces in their tertiary and quaternary structures which prevent degradation during digestion.

Numerous theoretically allergenic proteins cannot survive the destructive environment of the digestive tract, thus do not trigger hypersensitive reactions.[39]

Acute response

In the early stages of allergy, a type I hypersensitivity reaction against an allergen, encountered for the first time, causes a response in a type of immune cell called a TH2 lymphocyte, which belongs to a subset of T cells that produce a cytokine called interleukin-4 (IL-4).

What does class 2 food allergy mean

These TH2 cells interact with other lymphocytes called B cells, whose role is the production of antibodies. Coupled with signals provided by IL-4, this interaction stimulates the B cell to start production of a large quantity of a specific type of antibody known as IgE. Secreted IgE circulates in the blood and binds to an IgE-specific receptor (a helpful of Fc receptor called FcεRI) on the surface of other kinds of immune cells called mast cells and basophils, which are both involved in the acute inflammatory response. The IgE-coated cells, at this stage, are sensitized to the allergen.[40]

If later exposure to the same allergen occurs, the allergen can bind to the IgE molecules held on the surface of the mast cells or basophils.

Cross-linking of the IgE and Fc receptors occurs when more than one IgE-receptor complicated interacts with the same allergenic molecule, and activates the sensitized cell. Activated mast cells and basophils undergo a process called degranulation, during which they release histamine and other inflammatory chemical mediators (cytokines, interleukins, leukotrienes, and prostaglandins) from their granules into the surrounding tissue causing several systemic effects, such as vasodilation, mucous secretion, nerve stimulation, and smooth-muscle contraction. This results in rhinorrhea, itchiness, dyspnea, and anaphylaxis.

What does class 2 food allergy mean

Depending on the individual, the allergen, and the mode of introduction, the symptoms can be system-wide (classical anaphylaxis), or localized to specific body systems.[40]

Late-phase response

After the chemical mediators of the acute response subside, late-phase responses can often happen due to the migration of other leukocytes such as neutrophils, lymphocytes, eosinophils, and macrophages to the initial site.

The reaction is generally seen 2–24 hours after the original reaction.[41] Cytokines from mast cells may also frolic a role in the persistence of long-term effects.[42]


Cause

Although sensitivity levels vary by country, the most common food allergies are allergies to milk, eggs, peanuts, tree nuts, seafood, shellfish, soy, and wheat.[18] These are often referred to as «the large eight».[19] Allergies to seeds — especially sesame — seem to be increasing in numerous countries.[20] An example an allergy more common to a specific region is that to rice in East Asia where it forms a large part of the diet.[21]

One of the most common food allergies is a sensitivity to peanuts, a member of the bean family.

Peanut allergies may be severe, but children with peanut allergies sometimes outgrow them.[22] Tree nuts, including almonds, brazil nuts, cashews, coconuts, hazelnuts, macadamia nuts, pecans, pistachios, pine nuts, and walnuts, are also common allergens. Sufferers may be sensitive to one specific tree nut or to numerous diverse ones.[23] Also, seeds, including sesame seeds and poppy seeds, contain oils where protein is present, which may elicit an allergic reaction.[23]

Egg allergies affect about one in 50 children but are frequently outgrown by children when they reach age five.[24] Typically, the sensitivity is to proteins in the white, rather than the yolk.[23]

Milk from cows, goats, or sheep is another common food allergen, and numerous sufferers are also unable to tolerate dairy products such as cheese.

A little portion of children with a milk allergy, roughly 10%, own a reaction to beef. Beef contains a little quantity of protein that is also present in cow’s milk.[25]

Seafood is one of the most common sources of food allergens; people may be allergic to proteins found in fish, crustaceans, or shellfish.[26]

Other foods containing allergenic proteins include soy, wheat, fruits, vegetables, maize, spices, synthetic and natural colors,[citation needed] and chemical additives.

What does class 2 food allergy mean

Balsam of Peru, which is in various foods, is in the «top five» allergens most commonly causing patch test reactions in people referred to dermatology clinics.[27][28][29]

Atopy

Food allergies develop more easily in people with the atopic syndrome, a extremely common combination of diseases: allergic rhinitis and conjunctivitis, eczema, and asthma.[33] The syndrome has a strong inherited component; a family history of allergic diseases can be indicative of the atopic syndrome.[medical citation needed]

Sensitization

Sensitization can happen through the gastrointestinal tract, respiratory tract and possibly the skin.[30] Damage to the skin in conditions such as eczema has been proposed as a risk factor for sensitization.[31] An Institute of Medicine report says that food proteins contained in vaccines, such as gelatin, milk, or egg can cause sensitization (development of allergy) in vaccine recipients, to those food items.[32]

Cross-reactivity

Some children who are allergic to cow’s milk protein also show a cross-sensitivity to soy-based products.[34] Some baby formulas own their milk and soy proteins hydrolyzed, so when taken by infants, their immune systems do not recognize the allergen and they can safely consume the product.

Hypoallergenic baby formulas can be based on proteins partially predigested to a less antigenic form. Other formulas, based on free amino acids, are the least antigenic and provide finish nutritional support in severe forms of milk allergy.

People with latex allergy often also develop allergies to bananas, kiwifruit, avocados, and some other foods.[35]


Diagnosis

Diagnosis is generally based on a medical history, elimination diet, skin prick test, blood tests for food-specific IgE antibodies, or oral food challenge.[1][2]

  1. For skin-prick tests, a tiny board with protruding needles is used.

    The allergens are placed either on the board or directly on the skin. The board is then placed on the skin, to puncture the skin and for the allergens to enter the body. If a hive appears, the person is considered positive for the allergy. This test only works for IgE antibodies. Allergic reactions caused by other antibodies cannot be detected through skin-prick tests.[43]

Skin-prick testing is simple to do and results are available in minutes. Diverse allergists may use diverse devices for testing. Some use a «bifurcated needle», which looks love a fork with two prongs. Others use a «multitest», which may glance love a little board with several pins sticking out of it.

In these tests, a tiny quantity 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 little quantity 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 excellent for quickly learning if a person is allergic to a specific food or not, because it detects IgE. Skin tests cannot predict if a reaction would happen or what helpful of reaction might happen if a person ingests that specific allergen. They can, however, confirm an allergy in light of a patient’s history of reactions to a specific food.

Non-IgE-mediated allergies cannot be detected by this method.

  1. Patch testing is used to determine if a specific substance causes allergic inflammation of the skin. It tests for delayed food reactions.[44][45][46]
  2. Blood testing is another way to test for allergies; however, it poses the same disadvantage and only detects IgE allergens and does not work for every possible allergen. Radioallergosorbent testing (RAST) is used to detect IgE antibodies present to a certain allergen. The score taken from the RAST is compared to predictive values, taken from a specific type of RAST.

    If the score is higher than the predictive values, a grand chance the allergy is present in the person exists. One advantage of this test is that it can test numerous allergens at one time.[47]

A CAP-RAST has greater specificity than RAST; it can show the quantity of IgE present to each allergen.[48] Researchers own been capable to determine «predictive values» for certain foods, which can be compared to the RAST results. If a person’s RAST score is higher than the predictive worth for that food, over a 95% chance exists that patients will own an allergic reaction (limited to rash and anaphylaxis reactions) if they ingest that food.[citation needed] Currently,[when?] predictive values are available for milk, egg, peanut, fish, soy, and wheat.[49][50][51] Blood tests permit 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. Other widely promoted tests such as the antigen leukocyte cellular antibody test and the food allergy profile are considered unproven methods, the use of which is not advised.[52]

  1. Food challenges test for allergens other than those caused by IgE allergens. The allergen is given to the person in the form of a pill, so the person can ingest the allergen directly.

    What does class 2 food allergy mean

    The person is watched for signs and symptoms. The problem with food challenges is that they must be performed in the hospital under careful watch, due to the possibility of anaphylaxis.[53]

Food challenges, especially double-blind, placebo-controlled food challenges, are the gold standard for diagnosis of food allergies, including most non-IgE-mediated reactions, but is rarely done.[54] 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.[medical citation needed]

The recommended 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 own been noted after food ingestion. If the allergist feels the symptoms or reactions are consistent with food allergy, he/she will act out allergy tests. Additional diagnostic tools for evaluation of eosinophilic or non-IgE mediated reactions include endoscopy, colonoscopy, and biopsy.[medical citation needed]

Differential diagnosis

Important differential diagnoses are:

  1. Irritable bowel syndrome
  2. Lactose intolerance generally develops later in life, but can present in young patients in severe cases. It is due to an enzyme deficiency (lactase) and not allergy, and occurs in numerous non-Western people.
  3. Celiac disease.

    While it is caused by a permanent intolerance to gluten (present in wheat, rye, barley and oats), is not an allergy nor simply an intolerance, but a chronic, multiple-organautoimmune disorder primarily affecting the little intestine.[55][56][57]

  4. C1 Esterase inhibitor deficiency (hereditary angioedema), a rare disease, generally causes attacks of angioedema, but can present solely with abdominal pain and occasional diarrhea.


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