Vol. 2, #15
April 16, 2005

Q: What are "food allergies" , do they really exist, and what can be done about them? - Technical

A: Food allergy is a reaction of the body's immune system to something in a food or an ingredient in a food; usually a protein. It can be a serious condition and should be diagnosed by a board-certified allergist. A true food allergy (also called "food hypersensitivity") and its symptoms can take many forms.

Symptoms of food allergy differ greatly among individuals. They can also differ in the same person during different exposures. Allergic reactions to food can vary in severity, time of onset, and may be affected by when the food was eaten.

Common symptoms of food allergy include skin irritations such as rashes, hives and eczema, and gastrointestinal symptoms such as nausea, diarrhea and vomiting. Sneezing, runny nose and shortness of breath can also result from food allergy. Some individuals may experience a more severe reaction called anaphylaxis.

Anaphylaxis is a rare but potentially fatal condition in which several different parts of the body experience allergic reactions. These may include itching, hives, swelling of the throat, difficulty breathing, lower blood pressure and unconsciousness.

Symptoms usually appear rapidly, sometimes within minutes of exposure to the allergen, and can be life threatening. Immediate medical attention is necessary when anaphylaxis occurs. Standard emergency treatment often includes an injection of epinephrine (adrenaline) to open up the airway and blood vessels.


  • 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 exacerbations of atopic dermatitis.

    • In addition, angioedema and flushing can be due to IgE-mediated food allergy.

    • Food allergy is rarely an etiology for chronic urticaria or angioedema.
  • Atopic dermatitis
    • Significant controversy surrounds the role of food allergy in the pathogenesis of atopic dermatitis. Studies show that a significant subset of patients with chronic atopic dermatitis (35-40%) have IgE-mediated food allergy contributing to their skin disease.

    • Both food-specific IgE-mediated and cellular mechanisms appear responsible for chronic eczematous inflammation.

    • Removal of a specific food allergen leads to resolution of clinical symptoms in affected patients; reintroduction of the food exacerbates the atopic dermatitis.

    • Prophylactic studies show that avoiding particular foods (eg, cow milk, eggs, peanuts) helps prevent the onset of atopic dermatitis.
  • Dermatitis herpetiformis
    • This is an unusual form of non-IgE cell-mediated hypersensitivity related to celiac disease. It manifests clinically with a chronic and intensely pruritic rash with a distribution that has some similarities to the typical rash distribution of atopic dermatitis.

    • Elimination of gluten from the diet often leads to resolution of skin symptoms.
  • IgE-mediated gastrointestinal food allergy
    • In their classic form, these food allergy reactions include immediate hypersensitivity and the oral allergy syndrome.

    • Specific gastrointestinal symptoms include nausea, vomiting, abdominal pain, and cramping. Diarrhea is found less frequently.
  • Oral allergy syndrome
    • The patient may develop a sensation of itching or tingling of the lips, tongue, palate, and throat following the ingestion of certain foods. In addition, edema of the lips, tongue, and a sensation of tightness in the throat may be observed. In fewer than 5% of cases, symptoms progress to more systemic reactions.

    • In this syndrome, certain pollen and food allergy sensitivities are related. For example, individuals with ragweed allergy may experience oral allergy syndrome following the ingestion of bananas or melons, and patients with birch pollen allergy may experience this syndrome following the ingestion of raw carrots, celery, potato, apple, hazelnut, or kiwi.
  • Mixed IgE/non-IgE gastrointestinal food allergy (eosinophilic gastroenteritis)
    • Typical symptoms include postprandial nausea, abdominal pain, and a sensation of early satiety.

    • One of the hallmarks in children is 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 intestinal wall. While a dense eosinophil infiltrate may be seen anywhere from the lower esophagus throughout the large bowel, involvement is patchy and variable.

    • Ultimately, an elemental or oligoantigenic diet is necessary to aid in the diagnosis.

    • If the patient does not respond to the elemental diet, a trial of systemic oral corticosteroids can be useful for resolving the clinical symptoms.
  • Non-IgE-mediated gastrointestinal food allergy
    • Dietary protein enterocolitis is a syndrome that typically manifests in the first few months of life in a child who has severe projectile vomiting, diarrhea, and failure to thrive.

    • Cow milk and soy protein formulas are usually responsible for these reactions, which occur 2 or more hours after food ingestion.

    • Infants typically appear lethargic, wasted, and dehydrated. To establish the diagnosis, an oral challenge study must be performed.
  • Upper and lower respiratory tract reactions

    • These reactions typically include nasal congestion, sneezing, or rhinorrhea. They are usually observed in conjunction with skin or gastrointestinal symptoms.

    • IgE-mediated pulmonary symptoms may include rhinoconjunctivitis, laryngeal edema, cough, bronchospasm, and anaphylaxis.


    • 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 of the 279 children (24%) 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.

    • In a related report, 320 children with atopic dermatitis undergoing blinded food challenges at Johns Hopkins Hospital were monitored for respiratory reactions. Overall, 34 of 205 (17%) 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.

    • Wheezing as the only manifestation of an allergic reaction to food is rare.

    • Children with atopic dermatitis, especially those with food reactions confirmed during blinded food challenges, appear to have a higher risk for developing food-induced asthma.

    • The primary clinical effect is not acute bronchopulmonary obstruction, but chronic asthma symptoms or difficulty in controlling the asthma.

    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.
  • Severe anaphylactic reactions or fatality
    • Following the ingestion of food, severe anaphylactic reactions (ie, systemic allergic reactions) or fatality can occur.

    • Symptoms may include the following:

      • Oropharyngeal pruritus

      • Angioedema (eg, laryngeal edema)

      • Stridor

      • Cough

      • Dyspnea

      • Wheezing

      • Dysphonia

      • Urticaria

      • Emesis

      • A feeling of impending doom

      • Cardiovascular collapse
    • Risk factors include the following:

      • The presence of asthma, especially in patients with poorly controlled disease

      • Previous episodes of anaphylaxis with the incriminated food

      • Failure to recognize early symptoms of anaphylaxis

      • Delay or lack of immediate use of emergency medications (eg, epinephrine, antihistamines)

Of all the individuals who have any type of food sensitivity, most have food intolerances. Fewer people have true food allergy involving the immune system. Other reactions to foods are called food intolerance and food idiosyncrasy. Food intolerance and food idiosyncrasy reactions are generally localized, temporary, and rarely life threatening, whereas food allergy can cause life-threatening reactions.

 Adverse food reactions can be classified into 2 categories. The first is hypersensitivity that is an immunologically mediated adverse food reaction and is unrelated to any physiologic effect of the food or food additive. These reactions include disorders mediated by immunoglobulin E (IgE) antibodies (eg, IgE-mediated reaction to peanuts), which occur more immediately, and others resulting from non-IgE mechanisms (eg, non-IgE-mediated reactions such as protein-induced enterocolitis syndrome), which generally take several hours to appear clinically.

The second category is food intolerance. These reactions include any adverse physiologic response to a food or food additive that is not immunologically mediated (eg, lactose intolerance, bacterial food poisoning).

Allergic reactions to food are IgE-mediated or non-IgE-mediated. Immune responses mediated by specific IgE antibodies are the most widely recognized mechanism of food hypersensitivity. Patients with atopy produce IgE antibodies to specific epitopes in the food allergen. These antibodies bind to high-affinity IgE receptors on tissue mast cells and basophils that are present in the skin, gastrointestinal tract, and respiratory system. Subsequent allergen exposure binds these IgE antibodies and initiates the release of many mediators, including histamines, prostaglandins, and leukotrienes. This results in vasodilatation, smooth muscle contraction, and mucus secretion, which, in turn, lead to a spectrum of clinical symptoms observed in persons with allergic reactions to food.

Food allergens are typically water-soluble glycoproteins with molecular weights of 10-70 kd. These characteristics facilitate the absorption of these allergens across mucosal surfaces. Moreover, food allergens are generally resistant to proteolysis and are heat-stable. Several 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, specific IgE antibodies determined by skin prick or in vitro testing) and only rarely cross-react clinically. Finally, cross-reactive allergens have been identified among certain foods and airborne pollens  Conserved homologous proteins likely account for this cross-reactivity.

Food intolerance is an adverse reaction to a food substance or additive that involves digestion or metabolism (breakdown of food by the body) but does not involve the immune system. Lactose intolerance is an example of food intolerance. It occurs when a person lacks an enzyme needed to digest milk sugar. If a person who is lactose intolerant eats milk products, they may experience symptoms such as gas, bloating and abdominal pain.

Food idiosyncrasy is an abnormal response to a food or food substance. The reaction can resemble or differ from symptoms of true food allergy. Idiosyncratic reactions to food do not involve the immune system. Sulfite sensitivity or sulfite-induced asthma is an example of a food idiosyncrasy that affects small numbers of people in the population. However, sulfite-induced asthma can be potentially life threatening.

Other suspected adverse reactions to foods such as to corn, high fructose corn syrup and sugar have rarely been demonstrated as true food allergies. Some foods contain a variety of either naturally occurring or added components that can cause a chemical, or drug-like reaction. The "burning" sensation when eating foods like chili peppers is an example of a chemical food reaction.

You should see a board-certified allergist to get a diagnosis. An allergist and dietitian can best help the food-allergic patient manage diet issues with little sacrifice to nutrition or the pleasure of eating.

Making a diagnosis may include:

  • A thorough medical history;
  • The analysis of a food diary; and
  • Several tests including skin-prick tests, RAST tests (blood test) and food challenges (using different foods to test for allergic reactions).

Once a diagnosis is complete, an allergist will help set up a response plan to manage allergic reactions that may occur. A response plan may include taking medication by injection or drops ( sublingual-under the tonue) to control allergic reactions.

Food additives may also induce allergic reactions. Misconceptions abound regarding allergy to food additives and preservatives. Although some food components have been shown to trigger asthma or hives in certain people, these reactions are not the same as those observed with food.


  • Severe anaphylactic reactions, including fatality, can occur following the ingestion of food. Typical symptoms observed in a food-induced anaphylactic reaction involve the respiratory tract and include oropharyngeal pruritus, angioedema (eg, laryngeal edema), stridor, cough, dyspnea, wheezing, and dysphonia. Food allergy is confirmed in approximately one third of the patients with anaphylaxis presenting to the emergency department at the Mayo Clinic.
  • Peanuts, tree nuts, and shellfish are usually implicated in food-induced anaphylactic reactions.
  • Risk factors for 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 emergency medications (eg, epinephrine, antihistamines) to treat the allergic reaction

Because food allergy can be life threatening, the allergy-producing food must be completely avoided. If you, or someone else, are experiencing a severe food allergic reaction, call 911 (or an ambulance) immediately and execute your response plan.

Most life-threatening allergic reactions to foods occur when eating away from the home. It is important to explain your situation and needs clearly to your host or food server. If necessary, ask to speak with the chef or manager.

The Food and Drug Administration (FDA) requires that ingredients are listed on most food labels. Be sure to look at the listings on labels to determine the presence of the eight major allergens. Since food and beverage manufacturers are continually making improvements, food-allergic persons should read the food label for every product purchased, each time it is purchased.  The same equipment to manufacture one food product may be used to manufacture another food product so even though the offending food is not in the other product, it may contain enough residue to produce fatal reactions as has happened numerous times with peanut contamination.

Many different foods can cause food allergic reactions. However, most reactions to foods are not food allergies but some other type of food sensitivity.

Lab Studies:

  • Serum testing for specific IgE antibodies to foods
    • Specific IgE antibodies to foods can be measured by in vitro laboratory methods (eg, IgE radioallergosorbent testing), which offers advantages when dermatographism, generalized dermatitis, and a clinical history of severe anaphylactic reactions to a given food limit skin testing.
    • This form of testing provides information similar to prick skin tests, but it is more expensive and generally less specific.
    • The recently developed CAP System fluorescent-enzyme immunoassay (FEIA) (Pharmacia Diagnostics, Uppsala, Sweden) provides a more quantitative method of determining allergen-specific IgE to food allergens.
    • Compared with the outcome of well-controlled oral food challenges, results of the CAP system FEIA are generally similar to those of prick skin tests in predicting symptomatic food allergy.
    • Quantitating food-specific IgE antibodies with this automated system can help identify patients who are highly likely to have allergic reactions (>95%).
    • Published positive and negative predictive values using this system are available, and these values aid in making the diagnosis.
    • Currently, the predictive values of CAP System FEIA results are limited to several major food allergens (ie, egg, milk, peanut, fish) and based on a population of children with moderate-to-severe atopic dermatitis.
    • This type of testing may eliminate the need to perform oral food challenges in some patients suggested to have an IgE-mediated food allergy.
  • Peripheral serum measurements of eosinophils or total IgE concentrations: Results from these tests may support the diagnosis of food allergy, but 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.

Other Tests:

  • Diet diary
    • This is a chronological record of all food eaten and any associated adverse symptoms. It is inexpensive to undertake and allows patients to focus on their 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.
  • Elimination diet
    • This is mainly used in the treatment and prevention of food allergy.
    • It requires complete avoidance of certain foods or groups of foods for a given time period, usually 7-14 days, and also may be used in the diagnostic approach to food allergy.
    • Success depends on identifying the correct food allergen and completely eliminating it in all forms from the diet. This can be difficult if multiple foods are under consideration.
    • Additional limitations of this method include potential effects of patient or physician biases, questionable patient compliance, and the time-consuming nature of the endeavor.
  • Skin testing
    • 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 the testing technique, interpretation of the reaction, and concomitant use of medications (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).
    • This is a reliable method of excluding IgE-mediated food allergies. The negative predictive accuracy is greater than 95%; however, the positive predictive accuracy is generally less than 50%, which limits clinical interpretation of positive skin test results.
    • Positive skin test and clinical history findings must 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 during this type of testing is increased when compared to the prick or puncture method, and this intradermal skin testing should be avoided.

    • In addition, the results from this method are less specific compared to those from prick or puncture testing.
  • Tests with uncertain diagnostic value: The diagnostic value of performing the following tests is not currently supported by objective scientific evidence:
    • 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 this type of testing does not aid in diagnosis.


  • Food challenge confirmation of food allergy
    • This includes properly conducted elimination of and oral challenge with foods suggested to cause allergic reactions as based on the medical history, skin testing results, or in vitro testing results.
    • Of these procedures, the double-blind placebo-controlled food challenge (DBPCFC) is the best method to help diagnose and confirm food allergy and other adverse food reactions.
    • Conduct any food challenge in a clinic or hospital setting with available personnel and equipment for treating a systemic allergic reaction. Patients undergoing a food challenge must not be on beta-blocker medications. Obtain intravenous access in patients with history findings that indicate the potential for a systemic reaction.
    • If the history of the patient suggests an anaphylactic reaction is possible following food ingestion, do not perform an oral food challenge.
  • Open food challenge
    • This test involves the patient ingesting the suspected food, which is prepared in its usual, 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 contents.
    • The open food challenge is best used in clinical practice when patient or physician bias is minimal.
    • This type of challenge is typically used when the skin test results for the suspect food are negative or if a specific food reaction is unlikely.
    • Whenever the results are equivocal, perform a blinded challenge.
    • Patients 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, which is disguised 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.

    • This test may be useful for screening the patient for entry into studies in which history findings will be unequivocally confirmed by DBPCFC results.

    • Trained personnel and equipment necessary to treat anaphylactic shock must be available prior to undertaking this procedure because it may result in allergic reactions.
  • Double-blind placebo-controlled food challenge
    • DBPCFC involves ingestion of the suspected food, which is disguised so the patient and observer are unaware of the contents of the challenge.
    • This type of challenge is designed to reduce patient and observer bias and subjective attitudes during the procedure.
    • Always perform this challenge in a clinic or hospital setting.
    • Consider this the criterion standard for diagnosing food allergy, 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.
    • Do not perform a challenge if the patient has a clearly convincing history of a severe life-threatening anaphylactic reaction following the isolated ingestion of a specific food.


  • Consultation with a nutritionist or nutrition service is invaluable in the overall management. The restriction 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 workup of selected patients. For example, patients presenting 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.


  • A properly managed well-balanced elimination diet (eg, allergen restriction) can lead to resolution of symptoms and can help avoid nutritional deficiencies.

  • Educate the patient and family how to properly read food labels and to identify common words for the food allergen of concern (eg, casein and whey for milk).

  • With elimination diets, only exclude those foods confirmed to provoke the food allergy.

  • Recognize obvious and hidden sources of food allergens. Be aware of noningestion exposures or contact (eg, airborne allergens).

  • Anticipate the likely candidates for food allergen cross-contamination, such as the following:
    • 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 grains (25%)
    • Tree nuts and other nuts (>50%)
  • Avoid high-risk situations (eg, buffets, picnics), where accidental or inadvertent ingestion of food allergens can occur.


  • Developing intolerance
    • In general, most infants and young children outgrow or become clinically tolerant of their food hypersensitivities.
    • Well-controlled prospective investigations of food allergy in infants and children demonstrate that by following proper elimination diets, 85% of confirmed symptoms are resolved by age 3 years.
    • Adults with food allergy also lose their clinical allergic reactions to foods after implementation of appropriate food elimination diets.
    • Approximately one third of all children and adults lose their clinical reactivity to specific food allergens after 1-2 years of appropriate food allergen elimination therapy. Patients with allergies to peanuts, tree nuts, fish, and shellfish rarely lose their clinical reactivity.
  • Avoidance of allergen
    • How well the patient complies with the allergen avoidance diet seems directly associated with the ultimate clinical outcome (ie, development of oral tolerance.
    • Patients with allergic reactions to peanuts, tree nuts, shellfish, and fish rarely lose their clinical reactivity.
  • Breastfeeding
    • While exclusive breastfeeding is frequently promoted as a means of preventing food allergy and atopic disease in general, considerable controversy remains regarding the effectiveness of this practice.
    • Some investigations suggest that lactating mothers should eliminate highly allergenic foods (eg, peanuts, tree nuts, shellfish) that may induce life-long allergic sensitivity in their infants. Many allergenic foods can cross from the mother's blood into the mother's milk. 
    • Further studies are needed to clarify the role of early elimination diets and breastfeeding in the prevention of food allergy.
  • Vaccines
    • Recent 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.
    • 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. Test the patient's skin 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 safely given in a graded, multidose scheme. If results are negative, the vaccine may be administered in the routine 1-dose manner

Food sensitivities may be a...

  • food allergy,
  • food intolerance, or
  • food idiosyncrasy.

The eight most common food allergens are milk, eggs, peanuts (legumes,  NOT nuts) , tree nuts, soy, wheat, fish and shellfish.

If you, or someone else, are having a serious allergic reaction to a food, CALL 911! (or call an ambulance).

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DISCLAIMER:  The information in this column, is NOT intended to diagnose and/or treat any health related issues and is provided solely for informational purposes only. Consult the appropriate healthcare professional before making any changes to your healthcare regime. Even what may seem like simple changes in the diet for example, can interact with, and alter, the efficiency of medications and/or the body's response to the medications. Many herbs and supplements exert powerful medicinal effects. Neither the author, nor the website designers, assume any responsibility for the reader's use or misuse of this information.

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