Food allergy
Also listed as: Allergy - food
Approximately two out of five Americans believe that they are allergic to certain foods. However, less than 1% have true food allergies. A food allergy occurs when the body's immune system reacts to otherwise harmless substances in certain foods. This is different from a food intolerance, which does not involve the immune system. While most food allergies are mild, in some cases they can cause anaphylactic shock, a serious, sometimes life-threatening reaction. Food allergies affect mostly young children. With the exception of peanut allergy, the majority of children outgrow their food sensitivities.
Signs and Symptoms
Many people who think they have food allergies actually have food intolerances. Symptoms of a true food allergy usually involve the skin and intestines and typically begin just after eating and not longer than two hours following ingestion of the particular food. Common symptoms include:
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Hives, itching, or eczema
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Nausea and vomiting, stomach cramps, indigestion, or diarrhea
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Swelling of the eyelids, face, lips, tongue, throat, or other parts of the body (called angioedema)
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Wheezing, nasal congestion, or trouble breathing
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Lightheadedness, dizziness, or fainting
When the symptoms listed above are extreme, they can be life-threatening. Call a medical emergency response unit if you see the following signs of extreme allergic reaction (anaphylactic shock):
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Swelling of the throat and difficulty swallowing
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Difficulty breathing
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Rapid pulse
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Dizziness, lightheadedness, or loss of consciousness
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Blue color to the skin and nails
Causes
In most cases, allergies occur when an individual who has a genetic sensitivity to certain allergens is exposed to the substance. Foods frequently responsible for food allergies include:
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Shellfish (such as shrimp, crab, and lobster)
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Tree nuts (namely, walnuts, almonds, and pecans)
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Peanuts (which are legumes, not true nuts)
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Fruits (particularly strawberries, but also melons, pineapple, and other tropical fruits)
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Tomatoes
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Fish
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Food additives (such as dyes, thickeners, and preservatives; monosodium glutamate [MSG] is a common food allergy in this category)
Foods that may cause intolerance include:
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Wheat and other gluten-containing grains
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Cows milk and other dairy products
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Corn products
Risk Factors
Family history of allergies increases your risk of having allergies, including food allergies. If both parents have food allergies, you have a 75% chance of having one yourself; one parent, 30 - 40%, and if neither parent has allergies, then you have a 10 - 15% chance.
Excessive exposure to a particular food — for example, in Japan where rice is a staple, rice is a common food allergen; in Scandinavia the common allergen is codfish; in India, chickpeas.
Diagnosis
A comprehensive history will be taken to find out what symptoms you experience after eating and how soon after eating they occur. Your doctor will also want to know how often you have the reaction and what type of medical treatment you received. Even if your symptoms seem clearly related to a specific food, your doctor may still want to do some tests to be sure that you have a true food allergy and to verify the food or foods responsible for your reaction.
The food causing the allergy can sometimes be identified by the following techniques:
Elimination and re-challenging diet (also called elimination and provocation diet).
This technique involves eliminating suspected foods from the diet one at a time until the symptoms disappear. If there is still a question about what may be causing the symptoms, then individual foods are reintroduced one at a time to see if an allergic reaction develops. (Note – this would not be done if the allergic reaction is dangerous or life threatening.) This method is not definitive, but may help narrow the list of suspected foods.
Skin testing
. A diluted amount of the food allergen is placed under the skin; if allergic, a raised, red skin lesion will appear, generally within 15 to 20 minutes.
Blood tests (RAST and ELISA).
These look for antibodies against the particular food allergens.
Preventive Care
Guidelines from reputable health agencies suggest some steps parents can take to reduce their child's chances of having food and other allergies, although there are no guarantees of success. If either or both parents have a personal or family history of allergy (for example, asthma, eczema, hay fever, perennial allergic rhinitis [allergy to animals, dust mites, or molds]) experts recommend the following:
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Avoid common allergenic foods, in particular peanuts and tree nuts, during pregnancy and while nursing -- peanut protein, as well as components of cow's milk, eggs, and wheat, are secreted into breast milk
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Breastfeed exclusively -- give your baby only breast milk for the first 6 months of life using hypoallergenic formulas to supplement breastfeeding if necessary
Note: Not all studies agree on exclusive breastfeeding. In fact, the latest and largest study investigating the relationship between breastfeeding and allergies, particularly asthma, suggests that breastfeeding in the early months of life can prevent allergies until your child is 2 years old.
However, breastfeeding may increase the risk of allergies once your child is older than 2 years. Since delaying foods allows the child's gastrointestinal tract to mature, the following strategies may be helpful:
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Delay giving your infant solid food until 6 months of age
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Delay giving your child common allergenic foods as follows: dairy until age 1 year; eggs until age 2 years; peanuts, nuts, and fish until 3 years
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If an allergy develops, carefully avoid the offending food
Treatment Approach
The goals of treatment are to reduce symptoms and avoid future allergic reactions. Once you are aware of the allergy, the best way to avoid a reaction is by not eating that food. Treatment at the time of a reaction varies according to the severity and type of symptoms. Mild symptoms may subside without treatment. Doctors generally recommend over the counter or prescription antihistamines to relieve mild itching, swelling, rash, runny nose, or headache. Soothing skin creams may provide some relief of rashes. Severe allergic reactions (anaphylactic shock) can come on suddenly and accelerate quickly; in this case, emergency treatment is needed. In some instances, survival may depend on an injection of epinephrine (adrenaline). Food allergy sufferers routinely learn to self-administer epinephrine, which may save their life. Avoiding the offending food is the best way to prevent future allergic reactions.
Lifestyle
Avoid offending foods. Read of all package ingredients carefully (many foods are processed with peanuts, eggs, or milk products such as whey); call ahead when eating out; and take your own food with you on trips.
If you have a history of anaphylactic shock, you should keep a preloaded syringe of epinephrine with you. Your doctor will teach you and a close family member how to use it should the need arise. You should wear a medical bracelet or necklace indicating your particular food allergies.
Medications
Antihistamines
. These are recommended for mild itching, swelling, rash, runny nose, or headache; available both by prescription and over the counter in many cold, sinus, and allergy remedies. These include diphenhydramine, cetirizine, clemastine , chlorpheniramine, desloratadine, fexofenadine, hydroxyzine, and loratadine. (Possible side effects include drowsiness, irritability, dry mouth, and heart palpitations.)
Skin creams
can help soothe rashes.
Epinephrine injection
is used to prevent anaphylactic shock. If you have a food allergy that causes such a serious reaction, your doctor will have you carry an injectable epinepherine pen and teach you, and those with whom you spend a lot of time, how to use it in an emergency.
Nutrition and Dietary Supplements
Although you should avoid foods that provoke an allergic reaction, you do not need to restrict variety in your diet. Studies show that the vast majority of people are allergic to only one or two foods. However, you should be aware of the families of foods to which you are allergic. For example, if you are allergic to walnuts, you may also be allergic to pecans and almonds; an allergy to shrimp may also indicate an allergy to crab.
Lactobacillus Acidophilus
L. acidophilus are bacteria that live in the intestines and vagina and protect against the entrance and growth of harmful organisms that cause disease. Some experts suggest that L. acidophilus may help lower the risk of allergies, including food allergies.
Lipase
Although scientific evidence is lacking, doctors may recommend lipase (a digestive enzyme responsible for the breakdown of fat) to treat food allergies.
Vitamin C
Some experts believe vitamin C may be helpful for allergic conditions such as food allergies. This application needs further study, but may be related to vitamin C’s ability to improve immune function.
Herbs
Herbal medicines have not been specifically tested for food allergies. However, there are a wide variety of herbs that a qualified herbal specialist might consider to help treat your food allergies and your symptoms based on his or her clinical experience. Examples of herbs such an expert might select are listed below. An herbal specialist might consider each of these herbs because of its ability to treat either allergies in general or stomach symptoms:
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Chamomile, German (
Matricaria recutita
)
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Dandelion (
Taraxacum officinale
)
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Evening Primrose (
Oenothera biennis
)
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Flaxseed (
Linum usitatissimum
)
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Peppermint (
Mentha x piperita
)
Like medications, herbs may produce side effects or interact with other substances including drugs. They should be used with caution and only under the guidance of a professionally trained and qualified herbalist.
Acupuncture
The American Academy of Medical Acupuncture endorses the use of acupuncture for allergies such as food allergies. Acupuncture can help restore normal immune function.
Homeopathy
Although very few studies have examined the effectiveness of specific homeopathic therapies, professional homeopaths may consider individualized remedies for the treatment of food allergy based on their knowledge and experience. Before prescribing a remedy, homeopaths take into account a person's constitutional type. A constitutional type is a person's physical, emotional, and psychological makeup. An experienced homeopath assesses all of these factors when determining the most appropriate treatment for each individual.
Other Considerations
Pregnancy
Women who have a food allergy or a partner with a food allergy may be able to reduce the risk of allergy in their child by avoiding common allergenic foods during pregnancy and nursing.
Prognosis and Complications
Food allergies may cause symptoms ranging from mild abdominal discomfort to life-threatening anaphylaxis. Avoiding offending foods may be easy if the food is uncommon or easily identified. However, successful avoidance of offending foods requires strict reading of all package ingredients and detailed inquiries when eating away from home. Children may outgrow food allergies (particularly to milk or soy), but adults are unlikely to lose their allergies.
Supporting Research
Carey CF, Lee HH, Woeltje KF, eds.
The Washington Manual of Medical Therapeutics.
29th ed. New York, NY: Lippincott-Raven; 1998:216-217, 223-225.
Chandra RK. Food allergy.
Indian J Pediatr
. 2002;69(3):251-255.
Friedrich MJ. A bit of culture for children: probiotics may improve health and fight disease.
JAMA
. 2000;284(11):1365-1366.
Kalliomaki M, Salminen S, Arvilommi H, Kero P, Koskinen P, Isolauri E. Probiotics in primary prevention of atopic disease: a randomized placebo controlled trial.
Lancet
. 2001;357(9262):1076-1079.
Hourihane JO. Recent advances in peanut allergy.
Curr Opin allergy Clin Immunol
. 2002;2(3):227-231.
Patil SP, Napihadkar PV, Bapat MM. Chickpea: a major food allergen in the Indian subcontinent and its clinical and immunochemical correlation.
Ann Allergy Asthma Immunol
. 2001;87(2):140-145.
Sampson HA. Clinical practice. Peanut allergy.
N Engl J Med
. 2002;346(17):1294-1299.
Sampson HA. Food allergy.
JAMA
. 1997; 278:1888-1894.
Sears MR, Greene JM, Willan AR, et al. Long-term relation between breastfeeding and development of atopy and asthma in children and young adults: a longitudinal study.
Lancet
. 2002;360:901-907.
Vadas P, Wai Y, Burks W, Perelman B. Detection of peanut allergens in breast milk of lactating women.
JAMA
. 2001;285(13):1746-1748.
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Review Date:
9/30/2005
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Reviewed By: Amy Paturel, MS, MPH. Previously reviewed by: Jacqueline A. Hart, MD, Department of Internal Medicine, Newton-Wellesley Hospital, Boston, Ma; Peter Hinderberger, MD, PhD, Ruscombe Mansion Community Health Center, Baltimore, MD; Richard A. Lippin, MD, President, The Lippin Group, Southampton, PA; Terry Yochum, DC, Rocky Mountain Chiropractic Center, Arvada, CO.
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