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Food Allergies

  • Definition

    An allergy is an immune reaction to a foreign antigen (often protein) - in this case, to a food item.


    Do you start itching whenever you eat peanuts? Does seafood cause your stomach to churn? Symptoms like these cause millions of Americans to suspect that they have a food allergy. But true food allergies affect a small percentage of people. Experts estimate that only 2 percent of adults, and from 2 to 8 percent of children, are truly allergic to certain foods.

    Food allergy is different from food intolerance, and the term is sometimes used in a vague, all-encompassing way, muddying the waters for people who want to understand what a real food allergy is. True food allergies are serious and, in rare cases, can be fatal.

    Intolerance to milk and other foods is much more common and usually less serious than allergy. Food intolerances may produce symptoms similar to food allergies, such as abdominal cramping. But while people with true food allergies must avoid certain offending foods altogether, people with food intolerance can often eat small amounts of the offending food without experiencing symptoms.

    lactose intolerance is sometimes mistaken for milk allergy. lactose intolerance is a problem of digestion due to an enzyme deficiency, with cramps and diarrhea the common hallmarks.

    Food allergies are much more common in infants and young children, who often later outgrow them. Increased susceptibility of young infants to food allergic reactions is believed to be the result of immunologic immaturity and, to some extent, intestinal immaturity. Older children and adults may lose their sensitivity to certain foods if the responsible food allergen can be identified and eliminated from the diet, although some food allergies can last a lifetime. Certain particular food allergies of childhood tend to persist, including peanuts, tree nuts, and shellfish. Children typically outgrow allergies to wheat, soy, milk, eggs, and other foods.


    By the mid-1920s, allergists had defined food allergy as an abnormal response of the immune system to an otherwise harmless food.

    Food allergens, those parts of food causing allergic reactions, are usually proteins. When the allergen passes from the mouth into the stomach, the body recognizes it as a foreign substance, producing antibodies to halt the invasion.


    The most common sites allergy symptoms are the mouth (swelling of the lips or tongue, itching lips), digestive tract (stomach cramps, vomiting, diarrhea), the skin (hives, rashes or eczema), and the airways (wheezing or breathing problems).

    Repeated exposure to allergens starts sensitizing those who are susceptible. Cow's milk, eggs, wheat, and soy are the most common food allergies in children. An early peanut allergy may be lifelong. Adults usually are most affected by nuts, fish, shellfish, and peanuts.

    Danger Of anaphylaxis

    The greatest danger in food allergy comes from anaphylaxis, a violent allergic reaction involving a number of parts of the body simultaneously.

    Anaphylaxis usually occurs after a person is exposed to an allergen to which he or she was sensitized by previous exposure (that is, it does not usually occur the first time a person eats a particular food).

    Although any food can trigger anaphylaxis (also known as anaphylactic shock), peanuts, tree nuts, shellfish, milk, eggs, and fish are the most common culprits. As little as one-fifth to one-five-thousandth of a teaspoon of the offending food has caused death.

    Anaphylaxis can produce severe symptoms in as little as 5 to 15 minutes, although life-threatening reactions may progress over hours. Signs of a reaction include:

    • difficulty breathing
    • feeling of impending doom
    • swelling of the mouth and throat
    • drop in blood pressure
    • loss of consciousness

    The sooner anaphylaxis is treated, the greater the person's chance of surviving.

    The person should be taken to a hospital emergency room, even if symptoms seem to subside on their own. Experts advise people who are susceptible to anaphylaxis to carry medication, such as injectable epinephrine, with them at all times - and to check the medicine's expiration date regularly.


    Figuring out whether you really do suffer from food reactions, and determining whether they are allergies or intolerances, may take some detective work, and may require the help of a specialist. People who think they may react badly to one or more uncommon foods may find it simpler just to avoid them. But staying away from major food groups, such as dairy or wheat products, can be a nuisance, forcing you to read labels constantly and avoid numerous products that contain the possibly troublesome ingredients.

    If you are not sure which foods may be causing the problem, start by keeping a detailed record for several weeks of everything that you eat and any symptoms you experience. Then go over the diary to see whether a particular food or foods consistently preceded these symptoms.

    Watch for these signs of a true food reaction: specific symptoms such as swollen lips, rashes, or diarrhea, rather than vague complaints such as dizziness, weakness, or fatigue. Keep note of the time of onset of symptoms relatively soon after eating - a few minutes to two hours for most allergies, two to six hours for most intolerances.

    Your physician will take a complete medical history, perform a physical exam, and may order additional tests, including those to pinpoint the specific allergen.


    The basic principles of treating food allergy are:

    1. avoidance of the allergen

    2. symptomatic therapy

    Avoidance of specific foods is critical once a true food allergy has been diagnosed by your physician.

    Persons with peanut anaphylaxis can have a fatal reaction to ingestion of a minute amount of the food. The presence of peanut proteins may be unsuspected in some foods, so the patient must be extra vigilant when away from home.

    Soy-based formulas are available for infants with milk allergy. Patients allergic to soy, eggs, and milk must be extra vigilant because processed food may contain those ingredients labeled as 'natural flavorings' or 'seasonings.' A food diary as described above may be helpful.

    Your physician may recommend certain medications to control allergic symptoms.

    Experts advise people who are susceptible to anaphylaxis to carry medication with them at all times, such as injectable epinephrine, and to check the medicine's expiration date regularly.

    There is no good evidence that avoiding allergenic foods during pregnancy prevents the development of allergies. It is, however, reasonable for pregnant women to avoid peanuts if the unborn child is ‘high risk’ by having a close relative with food allergies (e.g., sibling, parent). While every parent should discuss the risks and benefits with their pediatrician, there are recommendations for so-called ‘high risk’ infants after birth: 1) breastfeeding can reduce the development of food allergy, 2) breastfeeding women should avoid peanuts and tree nuts, and try to avoid eggs and seafood, and 3) use of protein hydrolysate formulas after/to supplement breast feeding until 12 months. Further recommendations include delaying introduction of solid food until 6 months, cow’s milk until 12 months, eggs until 2 years, and peanuts, tree nuts, and seafood until 3 years. As these recommendations can be confusing, you should ask your doctor about whether or not your infant is ‘high risk’ and how to proceed.


    What is a food diary?

    Can a food intolerance turn into a more serious food allergy?

    If one reaction is just dizziness and faintness, can the next exposure be fatal?

    What home treatment do you recommend in case of a reaction?

    Should an emergency anaphylactic kit be kept in the home?

    What signs or symptoms indicate the need for immediate medical attention?