Food Allergies

Updated: Feb 05, 2020
  • Author: Scott H Sicherer, MD; Chief Editor: Michael A Kaliner, MD  more...
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Practice Essentials

Food allergies are immunologically mediated adverse reactions to foods. 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.

Signs and symptoms

Signs and symptoms of food-induced anaphylaxis can include the following:

  • Oropharyngeal pruritus

  • Angioedema (eg, laryngeal edema)

  • Stridor

  • Dysphonia

  • Cough

  • Dyspnea

  • Wheezing

  • Nausea

  • Vomiting

  • Diarrhea

  • Flushing

  • Urticaria

  • Angioedema

  • Ocular injection, ocular pruritus, conjunctival edema, periocular swelling

  • Nasal congestion, nasal pruritus, rhinorrhea, and sneezing

  • Abdominal pain

  • Feeling of impending doom

  • Cardiovascular collapse

Necessary elements of a thorough medical history include the following:

  • Complete list of all foods suspected of causing symptoms

  • Manner in which the food was prepared (cooked, raw, added ingredients)

  • Minimum quantity of food exposure required to cause the symptoms

  • Reproducibility of symptoms on exposure to the food

  • Personal or family history of other allergic disease

  • Factors that can potentiate a food-allergic reaction (eg, exercise, [1] nonsteroidal anti-inflammatory drugs [NSAIDs], or alcohol)

In addition, obtain a thorough description of each reaction, including the following:

  • Route of exposure (ingestion, skin contact, inhalation) and dose

  • Timing of symptom onset in relation to food exposure

  • All observed symptoms and each one’s severity

  • Duration of the reaction

  • Treatment provided and clinical response to treatment

  • Most recent reaction

Physical examination findings are most useful for the following:

  • Assessing nutritional status, growth parameters, and signs of other allergic disease

  • Helping to rule out other conditions that may mimic food allergy

See Clinical Presentation for more detail.

See All About Allergies: Be Ready for Spring, a Critical Images slideshow, to help identify a variety of allergens and symptoms.


Laboratory studies that may be helpful include the following:

  • Specific immunoglobulin E (IgE) antibody testing: Positive results primarily denote sensitization and may not confirm clinical allergy; specific laboratory tests for some food hypersensitivities are not available

  • Basophil histamine-release assays: These are limited primarily to research settings

Skin testing includes the following approaches:

  • Prick testing: This is the most common screening test for food allergy; negative predictive accuracy exceeds positive predictive accuracy (>90% vs < 50%)

  • Intradermal testing: Generally avoided, because of the risk of inducing a systemic reaction

  • Patch testing: Appears promising, but additional studies are needed and it is not recommended for routine practice

Diet-related diagnostic measures may be helpful, as follows:

  • Diet diary

  • Elimination diet (may be used for diagnostic as well as therapeutic purposes)

  • Food challenge confirmation of food allergy (may be open; single-blind; or double-blind, placebo-controlled)

See Workup for more detail.


There are currently no curative therapies for food allergy. The only proven treatment is strict dietary elimination of the offending food allergen. A properly managed, well-balanced elimination diet includes the following elements:

  • Education of patients and families regarding how to read food labels properly and identify common words used for indicating the presence of the food allergen of concern

  • Avoidance of cross-contact (eg, through shared utensils or fryers) of allergens with otherwise safe foods during meal preparation

  • Elimination of only those foods that are confirmed as provoking allergic reactions; both obvious and hidden sources of food allergens (eg, medications and cosmetics) must be considered

  • Consideration of potential exposures by route other than ingestion (eg, skin contact or inhalation)

  • Anticipation of potential candidates for food allergen cross-reactivity (eg, peanut and lupine or cow milk with sheep milk) [2]

  • Avoidance of high-risk situations where accidental or inadvertent ingestion of food allergens can occur (eg, buffets or picnics)

Adherence to avoidance measures notwithstanding, accidental or inadvertent ingestions may occur and lead to a reaction. Strategies for dealing with such a reaction include the following:

  • Creation of a concise written emergency management plan (see, copies of which should be available in appropriate places (eg, daycare, schools, work locations, and college dormitory advisors)

  • Use of medical identification jewelry indicating food allergies

  • Ensuring that the patient has an emergency contact number available

  • Provision of anticipatory guidance measures (eg, educating the patient about potential sources of accidental exposure)

Emergency medications include the following:

  • Injectable epinephrine: This is the drug of choice for initial management of a food-induced anaphylactic reaction; the patient should have self-injectable epinephrine readily available at all times and should be properly trained in its use

  • Antihistamines may be used for the treatment of mild symptoms

  • Bronchodilators may be used but should not be depended upon for anaphylaxis; epinephrine should be given

  • Histamine-2 blockers as adjunctive therapy

  • Corticosteroids as adjunctive therapy

  • Intravenous fluids for hypotension

  • Glucagon for refractory anaphylaxis

In severe anaphylaxis, ventilatory and circulatory support may be needed.

Oral or sublingual immunotherapy appears to be a promising therapeutic option. [3, 4]  The first immunotherapy for peanut allergy was approved by the FDA in 2020. [5]

See Treatment and Medication for more detail.



Food allergies are immunologically mediated adverse reactions to foods. Such allergies can result in disorders with an acute onset of symptoms following ingestion of the triggering food allergen (eg, anaphylaxis), as well as in chronic disorders (eg, atopic dermatitis, eosinophilic esophagitis). Symptoms observed in a food-induced anaphylactic reaction may involve the skin, gastrointestinal tract, and respiratory tract. (See Pathophysiology, Etiology, and Presentation.) [6]

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 (medically supervised, gradual test feedings) . Sesame appears to be an emerging allergen. (See Etiology and Workup.)

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. (See Workup.) [7]

Adverse reactions to food that are not immune mediated are not considered to be food allergies. An example is lactose intolerance, which is caused by a deficiency of lactase. Adverse reactions to foods can also occur from toxic (eg, bacterial food poisoning) or pharmacologic (eg, caffeine) effects.



Although anaphylaxis can occur without skin symptoms, cutaneous reactions 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 dermatitis

Controversy surrounds the role of food allergy in the pathogenesis of atopic dermatitis. [8] Studies show that among patients with moderate chronic atopic dermatitis, 35-40% have IgE-mediated food allergy. [9, 10] Food-specific IgE-mediated and cellular mechanisms appear responsible for chronic eczematous inflammation.

Removal of a specific food allergen may lead to reduction or resolution of clinical symptoms in affected patients; reintroduction of the food may then exacerbate the atopic dermatitis if it is food-responsive. [11, 12] 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. [13]

In a study of 619 exclusively breastfed infants, those with atopic dermatitis were significantly more likely to be sensitized to foods. [14, 15] In addition, a strong association between the severity of the dermatitis and sensitization was observed, and positive associations between atopic dermatitis and specific foods (egg, cow’s milk, and peanut) were found.

In addition to skin-prick testing against cow's milk, egg, cod fish, wheat, sesame, and peanut, infants in the study were screened for filaggrin loss-of-function (FLG) gene mutations. [15] FLG mutations were significantly associated with incidence of atopic dermatitis and higher median transepidermal water loss relative to dermatitis severity. Although children with atopic dermatitis were significantly more likely to be sensitized to foods, this effect was not related to FLG mutation inheritance.

Celiac disease

Celiac disease is the result of an immune response to gluten proteins in grain.

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. [16]

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)

Symptoms vary according to location of the 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. [17]

A complete blood count (CBC) 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.

Eosinophilic esophagitis is characterized by symptoms related to esophageal dysfunction, such as dysphagia and pain, and histologically by eosinophil-predominant inflammation. Pathologically, 1 or more biopsy specimens must show a peak of 15 or more eosinophils per high power field. Alternative explanations (eg, reflux) for symptoms/histopathologic abnormalities should be excluded.

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.

In addition to diet therapy (or in place of diet therapy), treatment with anti-inflammatory medications (eg, corticosteroids) may be needed. Eosinophilic esophagitis appears to be a chronic disease and fibrosis and stricture formation could occur. Updated diagnostic and treatment approaches have been proposed. [18]

Non–IgE-mediated gastrointestinal food allergy

Food protein–induced enterocolitis syndrome (FPIES) typically manifests in the first few months of life with severe projectile vomiting, diarrhea, and failure to thrive. [19] Cow milk and soy protein formulas are usually responsible for these reactions. However, solid foods may also trigger these reactions, especially rice and oats. [20]

When the allergen is removed from the diet, symptoms resolve. Reexposure prior to resolution results in a delayed (2h) onset of vomiting, lethargy, increase in the peripheral blood polymorphonuclear leukocyte count, and, later, diarrhea. Hypotension and methemoglobinemia may occur.

Infants with FPIES 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. [21] 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.


Although wheezing can occur during a food-allergic reaction, foods do not appear to be a common trigger for chronic asthma. [22, 23, 24]

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 allergies are primarily the result of immune responses to food proteins. (Allergic reactions to non-protein food additives are uncommon. [23] ) Normally, noninflammatory immune responses develop to ingested foods in a process called oral tolerance. [25, 26] 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. [27]

IgE antibody-mediated responses

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 in 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

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. [28] 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. [29] Celiac disease is the result of an immune response to gluten proteins in grains.

Characteristics of food allergens

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 cross-react immunologically (ie, lead to the generation of specific IgE antibodies detectable by skin prick or in vitro testing) but less frequently cross-react clinically. [2] Delayed allergic reactions to meat proteins have been attributed to reactions to carbohydrate moieties. [30]

Risk factors

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. [31, 7] Teenagers and young adults appear to be overrepresented in registries of food allergy fatalities and present a special risk group.



General surveys report that as many as 25–30% of households consider at least 1 family member to have a food allergy. [32, 33] However, this high rate is not supported by controlled studies in which oral food challenges are used to confirm patient histories.

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. [34]

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. [35]

Sex- and age-related demographics

Among children, males appear to be more affected; among adults, females are more frequently affected. [36] The prevalence of food allergies has been estimated to be up to 8% in infants and children and 3.7 % in adults. [37]

However, variations in prevalence have been reported according to method used (self report, testing, physician evaluation), geographic region, and foods included in the assessment. [38]

In a population-based survey study of 40,443 US adults, an estimated 10.8% were food allergic at the time of the survey, whereas nearly 19% of adults believed that they were food allergic. Nearly half of food-allergic adults had at least 1 adult-onset food allergy, and 38% reported at least 1 food allergy–related ED visit in their lifetime. [39]

Studies in the United States and the United Kingdom indicate a rise in peanut allergy among young children in the past decade. [36, 40] One study showed an increase of peanut allergy in children from 0.4% in 1997 to 0.8% in 2002. [36] Studies from Canada and the United Kingdom indicate allergy rates to peanut of over 1% in children. [41, 42]

A report from the US Centers for Disease Control and Prevention (CDC) indicated that among children aged 0–17 years, the prevalence of food allergies increased from 3.4% in 1997–1999 to 5.1% in 2009–2011, a 50% rise. [43]

Based on available studies, estimations of the rate of food allergies in children have been summarized as follows for common food allergens: [37]

  • Cow milk - 2.5%

  • Eggs - 1.3%

  • Peanuts - 0.8%

  • Wheat - 0.4%

  • Soy - 0.4%



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. [44]

Population-based studies generally show that 85% of young children outgrow their allergy to milk or egg by age 3-5 years. [44] However, studies reported from a referral center showed more persistence of egg, milk, and soy allergies, with only about 50% of patients resolving these allergies by age 8-12 years. [45, 46, 47] 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.

Children with non-IgE–mediated food allergies, such as proctocolitis and enterocolitis, typically resolve their food allergy in the first years of life. [48] Allergic eosinophilic esophagitis appears to be a persistent disorder. [49]

Morbidity and mortality

Severe anaphylactic reactions, including death, can occur following the ingestion of food. [31, 7] 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, although anaphylactic reactions to a wide variety of foods have been reported. Fatalities caused by reactions to milk have increasingly been noted. [7]


Patient Education


Patients should always carry a self-injectable device with epinephrine that has been properly stored and is current (ie, not expired). Ensure that the patient receives proper training regarding when and how to use the injection device. Patients should also have an H1-blocker medication (again, properly stored and not expired) in a syrup or chewable tablet form available. In addition, patients should be instructed to obtain immediate medical assistance (eg, call 911) in the event of anaphylaxis.

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

Avoidance of allergens

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, patients with food allergies should be 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. Educate patients about the potential for food allergens to be present in medications and cosmetics.

Support groups

Inform patients with food allergies how to identify and use support groups. One such organization is the Food Allergy Research and Education group.

Early detection and treatment

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 Research and Education 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 patient education information, see the Allergies Center, as well as Food Allergy and Severe Allergic Reaction (Anaphylactic Shock).