eMedicine Specialties > Allergy and Immunology > Major Allergic Diseases

Food Allergies

Scott H Sicherer, MD, Associate Professor of Pediatrics, Mount Sinai School of Medicine of New York University

Updated: Sep 2, 2009

Introduction

Background

Adverse food reactions can be broadly classified into 2 categories.¹ The first category consists of immunologically-mediated adverse reactions to foods that are termed food allergies. Food allergies can result in disorders with an acute onset of symptoms following ingestion of the triggering food allergen (eg, anaphylaxis) and in chronic disorders (eg, atopic dermatitis).

The second category is composed of adverse reactions that are not immune-mediated. An example is lactose intolerance caused by a deficiency of lactase. Adverse reactions to foods can also occur from toxic (eg, bacterial food poisoning) or pharmacologic (eg, caffeine) effects.

Pathophysiology

Food allergies are primarily the result of immune responses to food proteins.² Normally, noninflammatory immune responses develop to ingested foods in a process called oral tolerance.³ For reasons that remain unclear, but likely include environmental and genetic factors, tolerance may be abrogated, leading to adverse immune responses. While sensitization (eg, development of an immunoglobulin E [IgE] immune response) to an allergen has been primarily assumed to occur from ingestion, this may not always be the case. For example, oral allergy syndrome (pollen-food related syndrome) describes an allergic response to specific raw fruits or vegetables that share homologous proteins with pollens; the initial route of sensitization is respiratory exposure to pollen proteins rather than oral exposure to food proteins. The skin may be another potential route of sensitization.⁴  

IgE antibody – mediated responses are the most widely recognized form of food allergy and account for acute reactions. Patients with atopy produce IgE antibodies to specific epitopes (areas of the protein) of one or more food allergens. These antibodies bind to high-affinity IgE receptors on circulating basophils and tissue mast cells present throughout the body, including the skin, gastrointestinal tract, and respiratory tract.

Subsequent allergen exposure binds and cross links IgE antibodies on the cell surface, resulting in receptor activation and intracellular signaling that initiates the release of inflammatory mediators (eg, histamine) and synthesis of additional factors (eg, chemotactic factors, cytokines) that promote allergic inflammation. The effects of these mediators on surrounding tissues result in vasodilatation, smooth muscle contraction, and mucus secretion, which, in turn, are responsible for the spectrum of clinical symptoms observed during acute allergic reactions to food.

Cell-mediated responses to food allergens may also mediate allergic responses, particularly in disorders with delayed or chronic symptoms. For example, food protein – induced enterocolitis syndrome (FPIES), a gastrointestinal food allergy, appears to be mediated by T-cell elaboration of the cytokine tumor necrosis factor (TNF)-alpha.⁵ Persons with atopic dermatitis that flares with ingestion of milk have been noted to have T cells that, in vitro, express the homing receptor cutaneous lymphocyte antigen, which is thought to home the cell to the skin and mediate the response.⁶ Celiac disease is the result of an immune response to gluten proteins in grains; this disorder is reviewed in the eMedicine Pediatrics article Celiac Disease.

Food allergens are typically water-soluble glycoproteins resistant to heating and proteolysis with molecular weights of 10-70 kd. These characteristics facilitate the absorption of these allergens across mucosal surfaces. Numerous food allergens are purified and well-characterized, such as peanut Ara h1, Ara h2, and Ara h3; chicken egg white Gal d1, Gal d2, and Gal d3; soybean-Gly m1; fish-Gad c1; and shrimp-Pen a1. Closely related foods frequently contain allergens that crossreact immunologically (ie, lead to the generation of specific IgE antibodies detectable by skin prick or in vitro testing) but less frequently crossreact clinically.⁷ Recently, delayed allergic reactions to meat proteins have been attributed to reactions to carbohydrate moieties.⁸

Frequency

General surveys report that as many as 25-30% of households consider at least 1 family member to have a food allergy.^9,10 This high rate is not supported by controlled studies in which oral food challenges (a medically supervised, gradual test feeding) are used to confirm patient histories.^11,12 The actual prevalence of food allergies is estimated to be 5-6% in infants and children and 3.7 % in adults.¹³

However, comprehensive studies that include oral food challenges are few in number. Considering allergy to milk, egg, peanut, and seafood in a meta-analysis of 6 international studies using oral food challenges, estimated rates of 1-10.8% were obtained.¹⁴ In a meta-analysis including allergy to fruits and vegetables (excluding peanut), only 6 international studies included oral food challenges, and estimates of allergy varied widely from 0.1-4.3% for fruits and tree nuts to 0.1-1.4% for vegetables to under 1% for wheat, soy, and sesame.¹⁵

Studies in the United States and the United Kingdom indicate a rise in peanut allergy among young children in the past decade.^16,17 One study showed an increase of peanut allergy in children from 0.4% in 1997 to 0.8% in 2002.¹⁶ Recent studies from Canada and the United Kingdom indicate allergy rates to peanut of over 1% in children.^18,19

Based upon available studies, estimations of the rate of food allergies in children have been summarized as follows for common food allergens: cow milk, 2.5%; eggs, 1.3%; peanuts, 0.8%; wheat, 0.4%; and soy, 0.4%.¹³ Allergic reactions to non-protein food additives are uncommon.²⁰

Mortality/Morbidity

• Severe anaphylactic reactions, including death, can occur following the ingestion of food.^21,22,23,24 Symptoms observed in a food-induced anaphylactic reaction may involve the skin, gastrointestinal tract, and respiratory tract. Frequently observed symptoms include oropharyngeal pruritus, angioedema (eg, laryngeal edema), stridor, dysphonia, cough, dyspnea, wheezing, nausea, vomiting, diarrhea, flushing, urticaria, and angioedema. Fatalities result from severe laryngeal edema, irreversible bronchospasm, refractory hypotension, or a combination thereof.
• Peanuts, tree nuts, fish, and shellfish are the foods most often implicated in severe food-induced anaphylactic reactions, though anaphylactic reactions have been reported to a wide variety of foods. Fatalities caused by reactions to milk are increasingly noted.²²
• Risk factors or associations for fatal food-induced anaphylaxis include: (1) the presence of asthma, especially in patients with poorly controlled disease; (2) previous episodes of anaphylaxis with the incriminated food; (3) a failure to recognize early symptoms of anaphylaxis; and (4) a delay or lack of immediate use of epinephrine to treat the allergic reaction.^21,22,23,24 Teenagers and young adults appear to be overrepresented in registries of food allergy fatalities and present a special risk group.

Race

• No predilection is known.

Sex

• Among children, males appear to be more affected; among adults, females are more frequently affected.¹⁶

Age

• In infants and children younger than 3 years, the prevalence of food allergy is approximately 5-6%.¹³
• The estimated prevalence in adults is approximately 3.7%.¹³

Clinical

History

• Necessary elements of a thorough medical history
  • Develop a complete list of all foods suspected to cause symptoms.
  • Discuss the manner of preparation of the food (cooked, raw, added spices or other ingredients).
  • Determine the minimum quantity of food exposure required to cause the symptoms.
  • Determine the reproducibility of symptoms upon exposure to the food.
  • Obtain a thorough description of each reaction, including the following:
    • The route of exposure (ingestion, skin contact, inhalation) and dose
    • The timing of the onset of symptoms in relation to food exposure
    • All observed symptoms and each one’s severity
    • The duration of the reaction
    • The treatment provided and the clinical response to treatment
    • The most recent reaction
  • Inquire about a personal or family history of other allergic disease.
  • Inquire about eliciting factors that can potentiate a food-allergic reaction (eg, exercise²⁵ , nonsteroidal anti-inflammatory drugs [NSAIDs], alcohol)

Clinical manifestations and disorders²⁶

• Cutaneous reactions
  • These are the most common clinical manifestations of an allergic reaction to a food or food additive.
  • Symptoms range from acute urticaria (most common) to flushing to angioedema to exacerbations of atopic dermatitis.
  • Food allergy is rarely the cause of chronic urticaria or angioedema.
• Atopic dermatitis²⁷
  • Controversy surrounds the role of food allergy in the pathogenesis of atopic dermatitis. Studies show that of patients with moderate chronic atopic dermatitis, 35-40% have IgE-mediated food allergy.^28,29
  • Both food-specific IgE-mediated and cellular mechanisms appear responsible for chronic eczematous inflammation.
  • Removal of a specific food allergen leads to reduction or resolution of clinical symptoms in affected patients; reintroduction of the food exacerbates the atopic dermatitis.^30,31 Reintroduction of a suspected food allergen should be performed under medical supervision because, in some instances, initial reintroduction of the food after a period of dietary elimination has resulted in more significant symptoms than were observed when the food was regularly ingested.³²
  • Prophylactic studies show that avoiding particular foods (eg, cow milk, eggs, peanuts) helps delay the onset of atopic dermatitis.³³
• Celiac disease: Celiac disease is the result of an immune response to gluten proteins in grain. This disorder is reviewed in the eMedicine Pediatrics article Celiac Disease.
• Dermatitis herpetiformis
  • This is a form of non-IgE cell-mediated hypersensitivity related to celiac disease. It is a blistering skin disorder that manifests clinically with a chronic and intensely pruritic rash with a symmetrical distribution.
  • Elimination of gluten from the diet usually leads to resolution of skin symptoms.
• IgE-mediated gastrointestinal food allergy
  • These food allergy reactions include immediate hypersensitivity reactions and the pollen-food allergy syndrome (oral allergy syndrome).
  • Specific gastrointestinal symptoms include nausea, vomiting, abdominal pain, and cramping. Diarrhea is found less frequently.
• Pollen-food allergy syndrome (oral allergy syndrome)
  • Patients with this syndrome develop itching or tingling of the lips, tongue, palate, and throat following the ingestion of certain foods. In addition, edema of the lips, tongue, and uvula and a sensation of tightness in the throat may be observed. In fewer than 3% of cases, symptoms progress to more systemic reactions, such as laryngeal edema or hypotension.³⁴
  • This syndrome is caused by cross-reactivity between certain pollen and food allergens. For example, individuals with ragweed allergy may experience oropharyngeal symptoms following the ingestion of bananas or melons, and patients with birch pollen allergy may experience these symptoms following the ingestion of raw carrots, celery, potato, apple, peach or hazelnut.
• Mixed IgE/non-IgE gastrointestinal food allergy (eosinophilic esophagitis and gastroenteritis)³⁵
  • Symptoms vary according to location of eosinophilia. Typical symptoms include postprandial nausea, abdominal pain, and a sensation of early satiety. Eosinophilic esophagitis may manifest as reflux symptoms and dysphagia; food impaction can occur as well.
  • Children may experience weight loss or failure to thrive.
  • CBC count and differential findings may show eosinophilia in approximately 50% of patients; however, this is not diagnostic. Typically, endoscopy and biopsy must be performed in order to establish the presence of eosinophils in the affected segment of the gut. While a dense eosinophil infiltrate may be seen anywhere from the lower esophagus through the large bowel, involvement is patchy and variable.
  • An elemental (no potential allergens) or oligoantigenic diet (a diet that removes common allergenic foods) and trials of food elimination may be required to determine the role of foods in a patient's condition. Eosinophilic esophagitis does not respond to acid blockade therapy.
  • In addition to diet therapy (or in place of diet therapy), treatment with anti-inflammatory medications (eg, corticosteroids) may be needed.
• Non–IgE-mediated gastrointestinal food allergy
  • Food protein – induced enterocolitis syndrome typically manifests in the first few months of life with severe projectile vomiting, diarrhea, and failure to thrive.³⁶
  • Cow milk and soy protein formulas are usually responsible for these reactions. However, solid foods may also trigger these reactions, especially rice and oats.³⁷
  • When the allergen is removed from the diet, symptoms resolve. Re-exposure prior to resolution results in a delayed (2 h) onset of vomiting, lethargy, increase in the peripheral blood polymorphonuclear leukocyte count, and, later, diarrhea. Hypotension and methemoglobinemia may occur.
  • Infants who are chronically ingesting the allergen typically appear lethargic, wasted, and dehydrated. The presentation may mimic sepsis. An oral food challenge may establish the diagnosis but is not always needed if the history is clear. No other definitive diagnostic tests are available. 
  • Breastfed infants may have mucus and blood in their stool, attributed to food allergens ingested by the mother, primarily cow milk. This allergic proctocolitis does not typically lead to anemia and is not associated with vomiting or poor growth. Maternal exclusion of the allergen resolves the bleeding. Eosinophilic inflammation of the rectum is noted if a biopsy is performed.^38,2 Additional causes of bleeding (eg, infection, fissures) should be considered.  
• Upper and lower respiratory tract reactions
  • Upper respiratory reactions typically include nasal congestion, sneezing, nasal pruritus, or rhinorrhea. They are usually observed in conjunction with ocular, skin, or gastrointestinal symptoms.
  • IgE-mediated pulmonary symptoms may include laryngeal edema, cough, or bronchospasm.
• Asthma³⁹
  • The role of food allergy in the pathogenesis of asthma is a controversial area of investigation.
  • At the National Jewish Center for Immunology and Respiratory Medicine, 67 (24%) of the 279 children with a history of food-induced asthma were documented to have a positive result after a blinded food challenge, which included wheezing. Interestingly, only 5 (2%) of these patients had wheezing as their only objective adverse symptom.⁴⁰
  • In a related report, 320 children with atopic dermatitis undergoing blinded food challenges at Johns Hopkins Hospital were monitored for respiratory reactions. Overall, 34 (17%) of 205 children with positive results from food challenges developed wheezing as part of their reaction. Therefore, a conservative estimate is that 5-10% of patients with asthma have food-induced allergy symptoms.⁴¹
  • In a pediatric case-controlled study comparing 19 children who required ventilation for an exacerbation of asthma and 38 control subjects matched by sex, age, and ethnicity, coincident food allergy was found to be independently associated with life-threatening asthma.⁴²
  • Wheezing as the only manifestation of an allergic reaction to food is rare. 
• Food-induced pulmonary hemosiderosis (Heiner syndrome)
  • This is a rare disorder characterized by recurrent episodes of pneumonia associated with pulmonary infiltrates, hemosiderosis, gastrointestinal blood loss, iron deficiency anemia, and failure to thrive in infants.
  • While the precise immunologic mechanism is unknown, it is thought to be secondary to a non-IgE hypersensitivity process.
• Food-induced anaphylaxis
  • Following the ingestion of food, severe anaphylactic reactions (ie, systemic allergic reactions), including death, can occur.
  • Symptoms may include the following:
    • Oropharyngeal pruritus
    • Angioedema (eg, laryngeal edema)
    • Urticaria
    • Ocular injection, ocular pruritus, conjunctival edema, periocular swelling
    • Nasal congestion, nasal pruritus, rhinorrhea, and sneezing
    • Stridor
    • Dysphonia
    • Cough
    • Dyspnea
    • Wheezing, bronchospasm
    • Nausea
    • Emesis
    • Abdominal pain
    • Diarrhea
    • A feeling of impending doom
    • Cardiovascular collapse
  • Anaphylaxis can occur without skin symptoms²⁴
  • Food-associated, exercise-induced anaphylaxis describes a disorder in which exercise is tolerated and a food or foods are tolerated, but when exercise follows ingestion of a specific food or foods, anaphylaxis results.⁴³

Physical

• The physical examination findings are most useful for assessing overall nutritional status, growth parameters, and signs of other allergic disease, such as atopic dermatitis, allergic rhinitis, or asthma.
• Findings from a comprehensive physical examination can help rule out other conditions that may mimic food allergy.

Causes

• Any food protein can trigger an allergic response, and allergic reactions to a large number of foods have been documented; however, only a small group of foods account for most of these reactions.
• Eggs, milk, peanuts, soy, fish, shellfish, tree nuts, and wheat are the foods most often implicated in allergic reactions that have been confirmed in well-controlled blinded food challenges. Sesame appears to be an emerging allergen.
• Investigations of near-fatal or fatal anaphylactic reactions following food ingestion reveal that most are caused by peanuts, tree nuts, and shellfish, although milk has been increasingly reported.^24,22

Differential Diagnoses

Workup

Laboratory Studies

• Serum testing for specific IgE antibodies to foods⁴⁴
  • Specific IgE antibodies to foods can be quantified by in vitro laboratory methods. The term RAST (radioallergosorbent test) is antiquated because modern methods do not use radiation. This test and skin prick testing both measure food-specific IgE antibodies. This in vitro test may offer advantages when skin testing is limited by dermatographism, generalized dermatitis, or a clinical history of severe anaphylactic reactions to a given food.
  • This form of testing provides information similar to skin prick tests, but it is more expensive.
  • Studies have correlated the outcomes of physician-supervised oral food challenges with the test results. While the studies generally show increasing risks of reaction with increasing concentrations of allergen, the specific correlations vary among studies.^2,45,46
  • Studies (so far primarily using one brand of test system) have reported levels highly indicative of allergy (>95%).^45,47 However, specific results have varied among studies, which is probably due to differences in patient selection, interpretation of positive outcomes, and other factors. Only a few foods have been analyzed in this manner (primarily peanut, egg, and milk), and predictive results are different for the different foods.
  • Test systems vary with regard to measurements, and similarly reported results may not be equivalent.⁴⁸ The clinician should also be aware of different reporting units that are not interchangeable with one another (eg, class vs units vs percentage).
  • The concentration of food-specific IgE does not correlate very well with severity of an allergy.
• Peripheral serum measurements of eosinophils or total IgE concentrations: Results from these tests support but do not confirm the diagnosis of food allergy. Likewise, normal values do not exclude diagnosis.
• Basophil histamine-release assays: These tests are mainly limited to research settings and have not been shown conclusively to provide reproducible results useful for diagnostic testing in a clinical setting.
• Additional diagnostic tests are under study, for example, to determine if analysis of IgE epitope binding or IgE binding to particular proteins in a food provides additional diagnostic information.

Other Tests

• Diet diary
  • This consists of keeping a chronological record of all foods eaten and any associated adverse symptoms. It is an inexpensive endeavor that documents the frequency of symptoms and their occurrence in relationship to food ingestion. In addition, it encourages the patient to focus on his or her diet.
  • This record is occasionally helpful for identifying the food implicated in an adverse reaction; however, it is not usually diagnostic, especially when symptoms are delayed or infrequent.
  • Occasionally, review of the diet diary reveals that the patient is not experiencing a reaction even when eating, as an ingredient in other foods, a significant amount of a food to which he or she was thought to be allergic.
• Elimination diet
  • This is used for diagnostic as well as treatment purposes.
  • When used as a diagnostic tool, the elimination diet requires complete avoidance of suspected foods or groups of foods for a given time period (usually 7-14 d) while monitoring for an associated decrease in symptoms. The trial elimination diet may be most useful to evaluate chronic symptoms.
  • Success depends on identifying the correct food allergen and completely eliminating it from the diet.
  • Limitations of this method include potential effects of patient or physician biases, variable patient compliance, and the time-consuming nature of the endeavor.
  • When the elimination diet is used as treatment, identified food allergens are removed from the diet indefinitely unless evidence exists that the food allergy has resolved.
• Skin testing^49,26,50
  • Prick and puncture tests are the most common screening tests for food allergy and can even be performed on infants in the first few months of life. However, the reliability of the results depends on multiple factors, including use of the appropriate extracts and testing technique, accurate interpretation of the results, and avoidance of medications that might interfere with testing (eg, antihistamines).
  • When used in conjunction with a standard criterion of interpretation and appropriate controls (eg, histamine: positive; saline: negative), these tests provide useful and reproducible clinical information in a short period (ie, 15-20 min) with minimal expense and negligible risk to the patient.
  • This is a reliable method of excluding IgE-mediated food allergies. The negative predictive accuracy is generally greater than 90%; however, the positive predictive accuracy is generally less than 50%, which limits clinical interpretation of positive skin test results. Similar to in vitro testing, interpretation of test results must consider the clinical history (to assess prior probability) and other factors such as the likelihood, from epidemiologic observations, of the food being a trigger of allergy.
  • Similar to in vitro IgE testing, the larger the skin test wheal size, the more likely that a clinical allergy exists.^51,52
  • Positive skin test results, in addition to the suggestion of clinical reactivity based on the history, must often be confirmed by an oral food challenge unless the patient has a convincing history of significant food allergy.
• Intradermal skin testing
  • The risk of inducing a systemic reaction with this type of testing is increased in comparison to the prick or puncture method; as a result, intradermal skin testing to foods should be avoided.
  • In addition, the results obtained by using this method are less specific compared to those obtained by using prick or puncture testing.
• Patch tests
  • Patch tests are performed by exposing the skin to the food allergen for 24 hours under occlusion and then evaluating the area for erythema and papules in the subsequent 24-72 hours.
  • The test has been evaluated for diagnosis of food allergy in eosinophilic esophagitis,⁵³ enterocolitis,⁵⁴ and atopic dermatitis.⁵⁵
  • Some studies show promise for this technique, but additional studies are needed to better characterize the utility of the results.
• Some available tests have uncertain diagnostic value. The diagnostic value of performing the following tests is not currently supported by objective scientific evidence:⁴⁴
  • Results from food-specific immunoglobulin G (IgG) or IgG subclass antibody concentration testing have not been proven to be helpful with diagnosis.
  • Testing for food antigen-antibody complexes has no proven diagnostic value.
  • Performing leukocyte cytotoxic tests is not supported by objective scientific evidence.
  • Results from subcutaneous provocation and neutralization testing have not been proven to be helpful for diagnosis.
  • Kinesiology-based testing is not recommended because objective scientific evidence has indicated that this type of testing does not aid in diagnosis.

Procedures

• Food challenge confirmation of food allergy⁵⁶
  • A physician-supervised (medically supervised) oral food challenge involves gradual feeding of the suspected food with careful assessment for any symptoms. If symptoms occur, the feeding is discontinued and medications are administered.
  • Food challenges are typically preceded by a period of elimination of the suspected food. They are conducted when the patient is at a stable clinical baseline and not taking medications that could interfere with observation of symptoms (eg, antihistamines).
  • Of these procedures, the double-blind, placebo-controlled food challenge (DBPCFC) is the most reliable method to help diagnose and confirm food allergy and other adverse food reactions because it eliminates both patient and observer bias. However, in a clinical setting where minimal bias is suspected, open food challenges may be preferable because blinding of the food is often not required.
  • Conduct any food challenge in a clinic or hospital setting with the personnel and equipment necessary to treat a systemic allergic reaction available at all times. Patients undergoing a food challenge should not be taking beta-blocker medications or any medication that might interfere with the treatment of anaphylaxis. If indicated by risk assessment, obtaining intravenous access may be prudent.
  • Clinically indicated oral food challenges are not generally performed when the history and test results already support a current diagnosis of allergy to the target food.
  • The decision to proceed to an oral food challenge must consider many factors, including the likelihood of a reaction, the severity of a reaction if one were to occur, the need to obtain a definitive diagnosis, and social and nutritional factors, among others.
• Open food challenge
  • This test involves the patient ingesting the suspected food, prepared in its customary fashion (ie, the challenge food is not disguised in any way).
  • Both the patient and the observer (eg, physician, nurse) are aware of the food being ingested.
  • The open food challenge is best used in clinical practice when patient and physician bias is minimal.
  • Whenever the results are equivocal, perform a blinded challenge.
  • Patients with histories of a previous reaction should never perform an open food challenge at home, even if the chance they will develop severe symptoms is remote.
• Single-blinded food challenge
  • This challenge involves the patient ingesting the suspected food disguised in a challenge food so the patient is unaware of the contents.
  • This type of challenge, which is suitable for clinical practice and some research investigations, is designed to reduce patient bias during the procedure. However, subjective attitudes regarding the outcome of the challenge cannot be completely eliminated.
• Double-blind placebo-controlled food challenge⁵⁷
  • DBPCFC involves supervised gradual ingestion of the suspected food disguised in another food (or hidden in capsules). A food similar in taste and appearance but without the allergen is used as a placebo control. The feeding (potential allergen vs placebo) is randomized so that both the patient and the observer are unaware of the contents of the challenge at the time of the feeding and observation. Feeding of the allergen and placebo may be separated by hours or days.
  • This type of challenge is designed to reduce both patient and observer bias and subjective attitudes during the procedure.
  • This procedure is considered the criterion standard for diagnosing food allergy, and is used especially in research investigations. Currently, it is the only completely objective method for determining the validity of the history of an adverse reaction to a food.

Treatment

Medical Care

• Education
  • Education is of paramount importance for patients with food allergies.
  • Patients can obtain useful resource information by contacting the Food Allergy and Anaphylaxis Network (toll-free phone number is 800-929-4040).
  • Remember that appropriate restriction and complete avoidance of the relevant food allergen or allergens is the only current effective therapy.
• Elimination of food allergen
  • Once a food allergy is diagnosed, strict elimination of the offending food allergen from the diet and avoidance of any contact with the food by ingestion, skin contact, inhalation, or injection is necessary.
  • Elimination and strict avoidance is the only proven medical therapy for this allergic disease.
• Recognize the early signs and symptoms of an allergic reaction. Keep in mind that cutaneous, gastrointestinal, and respiratory symptoms are the most common clinical manifestations of food allergy.

Consultations

• Consultation with a board-certified allergist/immunologist should be considered when food allergy is suspected or confirmed.
• Consultation with a nutritionist or nutrition service is invaluable in the overall management. The elimination diet can be reviewed and appropriate substitutions can be recommended. Dietary deficiencies can be anticipated and prevented.
• Consultation with a gastroenterologist is also useful in the evaluation of selected patients. For example, patients who present with possible anatomic gastrointestinal abnormalities, eosinophilic esophagitis or gastroenteritis, failure to thrive, and malabsorption syndromes may benefit from consultation with both an allergist and a gastroenterologist.

Diet

• A properly managed well-balanced elimination diet (eg, allergen restriction) can lead to resolution of symptoms and help avoid nutritional deficiencies.
• Educate the patient and family about how to properly read food labels and identify common words used for indicating the presence of the food allergen of concern.
• US labeling laws now require major allergens (ie, egg, milk, wheat, soy, peanut, tree nuts, fish, crustacean shellfish) to be identified as ingredients on manufactured food products using plain English terms. Note that not all potential allergens are included and that some may be subsumed under terms such as s pices or natural flavor.
• Advisory labels (eg, may contain) are not regulated, are voluntary, and may reflect variable risks.
• Meal preparation must consider avoidance of crosscontact (eg, shared utensils, fryers) of allergens with otherwise safe foods.
• With elimination diets, only exclude those foods confirmed to provoke allergic reactions.
• Review obvious and hidden sources of food allergens. Be aware of the potential for exposures by routes other than ingestion, such as skin contact, or inhalation. This concern is particularly problematic for foods while they are being cooked and proteins are dispersed in the steam (eg, frying fish, boiling milk). Educate about the potential for food allergens to be present in medications and cosmetics.
• Anticipate potential candidates for food allergen crossreactivity, such as the following:⁷
  • Eggs and chicken (<5%)
  • Cow milk and beef (10%)
  • Cow milk and goat milk (>90%)
  • Fish (>50%)
  • Peanuts and related legumes (<10%)
  • Soy and related legumes (<5%)
  • Wheat and other grains (25%)
  • Tree nuts and other nuts (>50%)
• Encourage avoidance of high-risk situations (eg, buffets, picnics), where accidental or inadvertent ingestion of food allergens can occur.
• Instruct patients to discuss their food allergies with restaurant and food establishment personnel.

Medication

Despite following stringent avoidance measures for clinically relevant food allergens, accidental or inadvertent ingestions may occur. Therefore, patients must be instructed on actions to take in the event of a reaction. For persons with a potentially severe food allergy, prescription of self-injectable epinephrine is advised.²⁶

A concise written plan for the treatment of allergic reactions resulting from accidental exposure to the food should be developed. Examples of such a plan can be downloaded from www.foodallergy.org. For patients with a history of a mild reaction, such as urticaria and pruritus following the ingestion of a food allergen, treatment may be limited to an oral antihistamine. However, the potential for a more severe reaction on subsequent exposures must be taken into consideration because of the possibility of the ingestion of a larger dose than previously ingested or an unexpected or unrecognized increase in the patient’s degree of sensitivity.

If the patient has significant systemic symptoms, the treatment of choice is epinephrine administered by intramuscular injection in the lateral thigh.⁵⁸ Examples of systemic manifestations of food allergy include generalized urticaria, laryngeal edema, lower respiratory symptoms (eg, chest tightness, dyspnea, wheezing), and hypotension. Epinephrine should likely be administered to any patient with history of a severe allergic reaction as soon as ingestion of the food allergen is discovered and the first symptoms appear, possibly even before symptoms appear.

Patient must be educated regarding when to use their self-injector and the proper technique. They should be instructed to obtain immediate medical assistance (eg, call 911) in the event of anaphylaxis.

Epinephrine is the primary medication indicated to treat anaphylaxis. Patients should not depend upon bronchodilators or antihistamines to treat anaphylaxis, though these can be used as additional therapies.⁵⁹ For more information on the treatment of anaphylaxis, please see eMedicine article Anaphylaxis.

Caregivers of children should be instructed on identification and treatment of allergic and anaphylactic reactions.

Additional therapy during an allergic reaction includes antihistamines. A bronchodilator may be used as an adjunctive therapy for asthma. Although corticosteroids are often given for anaphylaxis, they are not believed to alter the early symptoms; theoretically, they may reduce late symptoms.

Advanced medical therapy of food allergen–induced anaphylaxis may include antihistamines; bronchodilators; histamine 2 (h2) blockers; corticosteroids; administration of intravenous fluids, glucagon, and oxygen; as well as ventilatory and circulatory support in severe anaphylaxis.

Adrenergic agonists

Used in the emergency management of systemic allergic reactions or anaphylaxis (eg, urticaria, angioedema, bronchospasm, cardiovascular collapse). Effects are immediate and dramatic. Appropriate use of this class of medication can be lifesaving, especially in the emergency management of anaphylaxis.

Epinephrine (Adrenaline, EpiPen, TwinJect)

DOC for treating anaphylaxis. Helps decrease symptoms of anaphylaxis by increasing systemic vascular resistance, elevating diastolic pressure, producing bronchodilation, and increasing inotropic and chronotropic cardiac activity. In addition, helps reduce urticaria, angioedema, laryngeal edema, and other systemic manifestations of anaphylaxis.

Dosing

Adult

0.3 mL IM (also traditionally given SC) of 1:1000 aqueous injected (usual range is 0.2-0.5 mL) q10-15min, not to exceed 3 doses; may need to decrease dose to 0.2 mL in elderly persons or those with known cardiac conditions
0.3 mL IM of 1:1000 dilution q10-15min; IV route (1:10,000) seldom used; not to exceed 0.25 mg; given very slowly and with extreme caution
0.3-mg self-injectable devices (EpiPen, Twinject 0.3 mg)

Pediatric

IM dosing in children based on weight or 0.01 mL/kg IM of 1:1000 dilution; not to exceed 0.3 mL IM 1:2000 dilution q10-15min
0.15-mg self-injectable devices (EpiPen Jr, Twinject 0.15 mg)

Interactions

Increases toxicity of beta- and alpha-blocking agents and that of halogenated inhalational anesthetics, ie, drugs that may sensitize the heart to arrhythmias

Contraindications

Documented hypersensitivity; cardiac arrhythmias, coronary artery insufficiency, or angle-closure glaucoma; local anesthesia in areas such as fingers or toes because vasoconstriction may produce sloughing of tissue; do not use during labor (may delay second stage of labor)

Precautions

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Dose may be decreased in elderly patients to 0.2 mL; may cause disturbing reactions such as fear, anxiety, tenseness, restlessness, throbbing headache, weakness, dizziness, pallor, respiratory difficulty, palpitation, tachycardia, tremor, and arrhythmia; use with caution in patients with cardiovascular disease, hyperthyroidism, and diabetes; properly train patients with use of self-injectable devices; advise patients to seek medical attention if using self-injectable devices to manage allergic reactions

Follow-up

Deterrence/Prevention

• Emergency plan
  • Provide a written emergency treatment plan for the patient. Have copies of this plan available in appropriate places (eg, daycare, schools, work locations, college dormitory advisors).
  • Patients with food allergies should be advised to obtain and wear medical identification jewelry indicating their food allergies.
  • Ensure that the patient has an emergency contact number available (eg, 911, their physician's office phone number, or a local emergency department) that can be used in the event of a major food-induced allergic reaction.
  • Anticipatory guidance measures cannot be overemphasized; for example, educate the patient about potential sources of accidental or inadvertent exposure to relevant food allergens (eg, daycare, school, travel, picnics, dining out).
• Emergency medications
  • Ensure that the patient has self-injectable epinephrine readily available at all times. Also ensure that the patient receives proper training regarding when and how to use the device. An antihistamine should also be available. Patients with food allergies and asthma should always have access to a rapid-acting bronchodilator.
  • Self-injectable epinephrine is typically available by prescription (ie, EpiPen, EpiPen Jr, Twinject 0.3 mg, Twinject 0.15 mg). These devices should be stored properly (avoiding extremes of temperature) and replaced before the expiration date.
  • Injectable epinephrine is the drug of choice for the initial management of a food-induced anaphylactic reaction.

Prognosis

• Developing tolerance
  • In general, most infants and young children outgrow or become clinically tolerant of their food hypersensitivities. Specifically, most "outgrow" allergies to milk, egg, soy and wheat. Allergies to peanut, tree nuts, fish, and shellfish are more persistent.⁶⁰
  • Population-based studies generally show that 85% of young children outgrow their allergy to milk or egg by age 3-5 years.⁶⁰ However, recent studies reported from a referral center showed more persistence of egg and milk allergies, with only about 50% of patients resolving these allergies by age 8-12 years.^61,62 Children continued to lose their allergy into adolescent years.
  • About 20% of infants and young children experience resolution of their peanut allergy by the time they reach school age.⁶³
  • Children with non-IgE – mediated food allergies such as proctocolitis and enterocolitis typically resolve their food allergy in the first years of life.⁶⁴
  • Allergic eosinophilic esophagitis appears to be a persistent disorder.⁶⁵
• Avoidance of allergen: Strict avoidance of allergen is generally required to prevent allergic reactions. Whether strict avoidance or accidental exposures alters the natural course of food allergy remains unclear.^66,67
• Prevention of atopic disease through diet⁶⁸
  • Numerous studies have evaluated the role of maternal/infant diet on outcomes of atopic disease (asthma, atopic dermatitis, food allergy), particularly through studies of infants at risk based upon family history of atopy (at least 1 first-degree relative with a documented atopic disease). Most studies have focused upon elimination of allergens or a delay in introducing them. However, limitations in study design and number of studies have limited the ability to draw firm conclusions on a number of potential interventions.
  • Evidence for a protective effect of maternal allergen avoidance during pregnancy or lactation is lacking; however, some evidence supports a reduction in atopic dermatitis when allergens are avoided during lactation.
  • For infants at risk, some evidence shows that exclusive breastfeeding for at least 3 months protects against wheezing in early life.
  • In studies of infants at risk who are not exclusively breastfed for 4-6 months, modest evidence shows that using specific extensively hydrolyzed casein-based or partially hydrolyzed whey-based formulas reduces the risk of (or delays) atopic dermatitis when compared to feeding with a whole cow milk protein – based formula. Soy formula does not appear to offer an advantage compared to whole cow milk – based infant formula.
  • No current convincing evidence supports the delay of specific allergenic foods beyond 4-6 months of life.
  • Once allergic disease is noted, allergen elimination may be needed for treatment.
  • Further studies are needed to clarify the role of early elimination diets and breastfeeding in the prevention of food allergy.

Patient Education

• Preparation
  • Patients should always carry an epinephrine self-injectable device that has been properly stored and is current (ie, not expired).
  • Patients should also have an H1-blocker medication (again, properly stored and not expired) in a syrup or chewable tablet form available.
• Avoidance of allergen
  • Complete avoidance of the offending food allergen is the best strategic approach and the only proven therapy once the diagnosis of food hypersensitivity is established; therefore, these patients should be properly taught to recognize relevant food allergens that must be eliminated from their diet.
  • Instruct the patient about the proper reading of food labels and the need to inquire about food ingredients when dining out.
  • If the patient is in doubt about a food or food ingredient, suggest avoidance of the food in question.
• Support groups
  • Inform patients with food allergies how to identify and use support groups.
  • One such organization is the Food Allergy and Anaphylaxis Network (10400 Eaton Place, Suite 107, Fairfax, VA, 22030-2208 USA; fax: 703-691-2713; phone: 703-691-3179 or 800-929-4040; email: faan@foodallergy.org). 
• Early detection
  • Educate patients regarding recognition of the early signs and symptoms of a food-induced allergic reaction, and provide them with a written management plan for successfully dealing with these reactions.
  • Write a specific list of clinical signs and symptoms to look for if a reaction may be occurring, and include a clear management plan. An excellent example of such a plan is available on the Food Allergy and Anaphylaxis Network Web site.
  • Demonstrate to the patient and family how to actually administer medications, especially injectable epinephrine, in the event of an allergic reaction. To accomplish this, use demonstration trainer devices in the clinic setting. Reinforce that if injectable epinephrine is administered, the patient must be immediately evaluated in a medical setting.
• For excellent patient education resources, visit eMedicine's Allergy Center and Allergic Reaction and Anaphylactic Shock Center. Also, see eMedicine's patient education articles Food Allergy and Severe Allergic Reaction (Anaphylactic Shock).

Miscellaneous

Medicolegal Pitfalls

• When performing oral food challenges, be prepared to recognize and treat adverse clinical symptoms immediately. Appropriately trained personnel and the necessary equipment for the treatment of anaphylactic shock must be available prior to and throughout the entire oral food challenge and observation period because of the risk of triggering an allergic reaction.
• Patients should never be instructed to perform a food challenge at home.
• Confirm negative results from a double-blind, placebo-controlled food challenge (DBPCFC) using an open feeding (open food challenge) of the food in question in its usual form and quantity before giving final advice on dietary restrictions.
• If the patient has a history of severe allergic reactions following the ingestion of food allergens, give specific advice in the form of a written emergency treatment plan. In addition, educate the patient on how to administer emergency medications (eg, injectable epinephrine, antihistamines) in the event of a severe life-threatening allergic reaction. Encourage patients (when appropriate) or caretakers to carry these medications at all times in case they are needed to manage symptoms.

Special Concerns

• Future therapeutics⁶⁹
  • No curative therapies currently for food allergy.
  • Injection immunotherapy is an accepted treatment for anaphylactic allergy to insect venoms and for environmental allergies, but poses a high risk for food allergies (anaphylaxis to injected native food proteins).
  • Studies are underway to determine if oral or sublingual immunotherapy is safe and effective for food allergy.
  • Studies are underway to determine whether therapies with modified food proteins are safe and effective.
  • Additional future therapeutics include investigations of anti-IgE antibodies, cytokine or anti-cytokine therapies, and evaluation of traditional Chinese medicine.
• Diagnosis²
  • The clinician must appreciate that a positive test for food-specific IgE primarily denotes sensitization; additional consideration of the history, the epidemiology of food allergic disease, crossreactivity, and the degree of positivity of tests must be evaluated to assist in diagnosis. A physician-supervised oral food challenge may be required for diagnosis.
  • Because specific laboratory tests for some food hypersensitivities are not available, diagnosing non–IgE-mediated food allergies (eg, cow milk–induced and soy-induced enterocolitis syndromes, allergic eosinophilic gastroenteritis) is more difficult than diagnosing IgE-mediated food allergies.
  • In cases of allergic eosinophilic gastroenteritis, a biopsy may need to be performed. Elimination diets with gradual reintroduction of foods and supervised oral food challenges are often needed to help identify the causative foods.
  • For food protein–induced enterocolitis syndrome, perform a food challenge with 0.15-0.30 grams of protein per kilogram of body weight of the implicated protein and observe the patient for several hours. Positive reactions (eg, profuse vomiting and diarrhea) are typically accompanied by a rise in the absolute neutrophil count of more than 3500 cells/mm³. Because of the potential for shock, these challenges are best performed in the hospital setting.
  • When the history of an allergic reaction to a food suggests that the onset of symptoms is delayed by hours or days following ingestion, adjust the timing and monitoring of the challenge to correspond to these characteristics.
  • The successful administration of oral food challenges to young children requires a great deal of preparation, patience, and creativity. Young children may refuse to ingest the challenged food. Prior planning with the family is important to choose proper vehicles (eg, juice, cereal, solid food) for disguising the challenged substance.
• Vaccines
  • Scientific data support the routine 1-dose administration of the measles-mumps-rubella vaccine to all patients with egg allergy, even those with severe anaphylactic reactions following egg ingestion.⁷⁰ In the child with a history of a previous reaction to the measles-mumps-rubella vaccine, consider the possibility of allergy to gelatin, neomycin, or another component of the vaccine.
  • If the patient has a clinical history of egg allergy and has experienced systemic reactions (eg, anaphylaxis) following the ingestion of egg, the administration of the influenza vaccine requires special diagnostic consideration.⁷¹ After reviewing risks and benefits, the patient's skin can be tested with diluted preparations of the influenza vaccine (ie, puncture skin testing and, if needed, intradermal skin testing). If skin test results with the vaccine are positive, the vaccine can be given in a graded, multidose scheme. If results are negative, the vaccine may be administered in the routine 1-dose manner.

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Keywords

food allergies, food allergy, adverse immunologic reactions to foods, allergic reactions to foods, food hypersensitivity, food intolerance, food allergy test, food allergy symptoms, food allergy rash, food allergy treatment, allergy foods, adverse food reactions, lactose intolerance, bacterial food poisoning, peanut allergy, protein-induced enterocolitis syndrome, proctocolitis, food hypersensitivity, allergen exposure, anaphylactic reactions, food-induced anaphylactic reaction, oral allergy syndrome, dietary protein enterocolitis, food-induced asthma, food-induced pulmonary hemosiderosis, Heiner syndrome, egg allergy, milk allergy, peanut allergy, soy allergy, fish allergy, shellfish allergy, tree nut allergy, wheat allergy, celiac disease, childhood food allergy, lactose intolerant

Contributor Information and Disclosures

Author

Scott H Sicherer, MD, Associate Professor of Pediatrics, Mount Sinai School of Medicine of New York University
Scott H Sicherer, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology and American Academy of Pediatrics
Disclosure: Nothing to disclose.

Medical Editor

Stephen C Dreskin, MD, PhD, Director of Allergy, Asthma, and Immunology Practice, Professor of Medicine, Departments of Internal Medicine and Immunology, University of Colorado Health Sciences Center
Stephen C Dreskin, MD, PhD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association for the Advancement of Science, American Association of Immunologists, American Association of Neuropathologists, American Association of Ophthalmic Pathologists, American Association of Oral and Maxillofacial Surgeons, American College of Allergy, Asthma and Immunology, Clinical Immunology Society, and Joint Council of Allergy, Asthma and Immunology
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Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: eMedicine Salary Employment

Managing Editor

Stephen C Dreskin, MD, PhD, Director of Allergy, Asthma, and Immunology Practice, Professor of Medicine, Departments of Internal Medicine and Immunology, University of Colorado Health Sciences Center
Stephen C Dreskin, MD, PhD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association for the Advancement of Science, American Association of Immunologists, American Association of Neuropathologists, American Association of Ophthalmic Pathologists, American Association of Oral and Maxillofacial Surgeons, American College of Allergy, Asthma and Immunology, Clinical Immunology Society, and Joint Council of Allergy, Asthma and Immunology
Disclosure: Genentech Consulting fee Consulting

CME Editor

Timothy D Rice, MD, Associate Professor, Departments of Internal Medicine and Pediatrics and Adolescent Medicine, Saint Louis University School of Medicine
Timothy D Rice, MD is a member of the following medical societies: American Academy of Pediatrics and American College of Physicians
Disclosure: Nothing to disclose.

Chief Editor

Michael A Kaliner, MD, Clinical Professor of Medicine, George Washington University School of Medicine; Chief, Section of Allergy and Immunology, Washington Hospital Center; Medical Director, Institute for Asthma and Allergy
Michael A Kaliner, MD is a member of the following medical societies: American Academy of Allergy Asthma and Immunology, American Association of Immunologists, American College of Allergy, Asthma and Immunology, American Society for Clinical Investigation, American Thoracic Society, and Association of American Physicians
Disclosure: Abbott Consulting fee Consulting; Alcon Consulting fee Consulting; Glaxo Consulting fee Consulting; Greer Consulting fee Consulting; Sanofi Consulting fee Consulting; Schering Consulting fee Consulting; Teva  Consulting; Meda Honoraria Speaking and teaching

The author and editors of eMedicine gratefully acknowledge the contributions of previous authors Dan Atkins, MD, and John M James, MD, to the development and writing of this article.

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