Food Allergy—It's Nothing to Sneeze At
The term food allergy is often misapplied, leading many people to believe that they are "allergic" to certain foods when a more accurate term would be “food intolerance.” In fact, food allergy symptoms are caused either by a hypersensitivity reaction or by simple food intolerance to specific components of a food. Symptoms of adverse reactions to food range from a simple rash to life-threatening anaphylaxis. Identification and avoidance of any foods that trigger a reaction is the only "cure" available for food allergy.
The American Academy of Allergy and Immunology reports that 30% of adults believe they are allergic to certain foods. However, studies have shown that true food allergy is really quite rare, affecting less than 2% of the population. Part of the confusion lies in the definition of food allergy.
What Is a Food Allergy?
There is unfortunately no precise definition for the term food allergy. Instead, medical professionals use the term food hypersensitivity. This refers to a specific allergic reaction that involves the immune system, is triggered by a particular food, and is reproducible. In other words, the same symptoms—for example, wheezing or rash—must occur each time the food is eaten.
Food intolerance, which is estimated to occur in about 16% of the population, is an adverse reaction to a food and doesn't involve the immune system. Food intolerance may be inconsistent; reactions to the suspected food may vary in severity with each exposure, or may not occur at all.
What Causes a Food Hypersensitivity Reaction?
Food hypersensitivity is triggered by allergens—food components (usually proteins) that react with the immune system. Many different allergens can be present in the same food. Cow's milk; eggs; shellfish (shrimp, crab, or lobster); nuts (peanuts, walnuts, cashews, Brazil nuts); legumes (peas, lentils, lima beans); corn; soy; and wheat are the allergens most likely to trigger food hypersensitivity reactions.
Food hypersensitivity, especially to cow's milk, is seen more often in children (about 5%) than in adults (less than 2%). Many children outgrow food hypersensitivities in later years, with sensitivity to milk, egg, and soy the most likely to wane over time. People who are sensitive to fish or nuts, however, will probably have to avoid those foods forever.
Why Reactions Occur
People who are "allergic" to certain foods are simply more sensitive to the allergens found in these foods. Allergic reactions to food result from the actions of a specific groups of proteins called antibodies. Antibodies, an important part of the body's defense system, are activated when the offending food is eaten. Their role is to recognize foreign invaders (antigens)—in this case, allergens—and to get rid of them.
Certain types of antibodies, known as IgE, are more highly reactive, and perhaps more abundant, in people with food hypersensitivity.
When IgE antibodies encounter a food allergen to which they are sensitized, they attach themselves onto the food proteins. This attachment causes the immune system to release mediators—chemical messengers that travel through the bloodstream to alert other organs to the presence of an unwelcome protein guest.
Release of these mediators causes the uncomfortable—or occasionally dangerous—symptoms of an allergic reaction. The extent of the reaction depends on the quantity of food eaten, age and health status, and the route taken by the mediators. The three most common reaction sites include:
Symptoms of allergic reaction in the skin include rash, urticaria (raised, red, and extremely itchy welts also known as hives), and angioedema, which is a swelling of the skin that results from leakage of fluid into tissues. Angioedema affects the skin and mucosal tissues of the face, lips, mouth, and throat, larynx, extremities, and genitalia. Itching and eczema (an itchy, scaly skin rash) are also common but usually occur several days after the offending food is ingested. Urticaria and angioedema are most commonly immediate reactions, typically occurring within minutes (sometimes seconds) of food ingestion.
Mediators that travel to the GI tract may cause symptoms along its entire length: swelling of the lips, itchy mouth or throat, nausea and vomiting, cramps and bloating, abdominal distention or intense abdominal pain, and diarrhea.
Anaphylactic shock is an extremely severe and life-threatening type of allergic reaction. The symptoms occur in rapid succession, progressing from itching or throat swelling to difficulty breathing, hypotension, and loss of consciousness or even death, if appropriate treatment is not immediately instituted.
Food allergies of all sorts, but particularly those involving the skin and respiratory tract, can be either immediate—occurring in minutes—or delayed for hours or even days after the food is eaten. In some extremely sensitive individuals, just the release of food proteins into the air (as occurs, for example, with opening a bag of peanuts) can provoke the onset of symptoms.
Adverse reactions to food that occur outside of the immune system are defined as food intolerances. Distinguishing food intolerance from food hypersensitivity is often difficult for the lay person, because the symptoms are quite similar. Food intolerances can be attributed to a number of different causes, including:
- Chemical additives including aspartame, dyes, nitrites, MSG, sulfites, and tartrazine
- Pharmacologic causes or reactions to naturally-occurring, drug-like substances in foods such as caffeine, alkaloids (found in mushrooms), or goitrogens (in cabbage)
- Enzyme deficiency, such as lactose intolerance (the inability to produce the enzyme lactase, which digests lactose sugar in milk)
- Psychological disorder, such as food aversion
- Idiosyncratic, meaning "cause unknown"
Treating Food Hypersensitivities
Diagnostic tests must be conducted to determine if a true food allergy is present. These might include:
- Skin prick test: Extracts of suspected food antigens are dropped on the skin and the area is pricked or scratched through the drop. A "positive" result (raised bump) proves that immune cells in the skin are reacting to the antigen.
- Immunoassay, radioallergosorbent test (RAST), and fluorescent enzyme immunoassay (FEIA) test: This blood test indicates the presence of IgE, the antibody most active in food hypersensitivity reactions. The test can help identify which foods to avoid by matching up specific food antigens and IgE antibodies.
- Challenge test: The patient is fed suspected foods under carefully controlled conditions, and any reactions are noted. This is dangerous, however, if he or she is at risk for an anaphylactic shock.
Dietary modification is the usual method of treating food hypersensitivity. The patient is asked to keep a food diary for 1-2 weeks, writing down all foods eaten and noting any reactions. Any suspected foods are then eliminated to see if the symptoms clear up. An elimination diet can become very limited, so the assistance of a registered dietitian (RD) should be enlisted. He or she can explain the diet and ensure that nutrition requirements are being met.
There are no existing cures for food hypersensitivity. Although allergy injections and antihistamine medications work for pollen or plant allergies, these remedies don't work against food hypersensitivities or food intolerances. Strict avoidance of offending foods is the only cure. This is a serious challenge. Imagine having to constantly worry about the content of restaurant dishes or having to read every last word on a food label to determine its ingredients!
When food hypersensitivity occurs, acute treatment may be required. In the face of anaphylaxis, such action may be life-saving. Immediate administration of epinephrine is necessary to stop the reaction. Further treatment in an emergency room or doctor’s office is generally required. This may include antihistamines, cortisone, or both.
While an initial anaphylactic reaction may not be severe, the second may be fatal because it occurs after the body has had time to build up antibodies specific to the offending food allergen. Consultation with an allergist is necessary to determine if you are at risk for this reaction. Most persons who have had significant anaphylactic reactions should always carry an automatic injector device, such as the Epi-pen, that allows them to rapidly treat symptoms while awaiting transport to an emergency facility.
Skin and respiratory reactions may sometimes be treated with antihistamines or lung inhalers. All hypersensitivity reactions in which there is swelling of the mouth or throat must be rapidly evaluated by qualified medical personnel to ensure that the swelling does not progress in such a way as to obstruct breathing.
Members of the Food Allergy Network say that convincing other people that food hypersensitivity is real is one of the most difficult problems they face. Fortunately, resources and support networks are available for those who must cope with a food allergy.
Allergy and Asthma Network/Mothers of Asthmatics
American Academy of Allergy, Asthma, and Immunology
American Academy of Pediatrics
Academy of Allergy and Immunology website. Available at: http://www.aaaai.org/.
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Last reviewed July 2007 by Marcin Chwistek, MD
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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