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Food Allergy by Rosalyn Carson-DeWitt, MD

Definition

A food allergy is an adverse or abnormal reaction to a food or a food additive.

Causes

A few specific foods seem to cause a majority of the food reactions. The most common triggers of a food reaction include:

Cow's milk
Eggs
Peanuts
Wheat
Soy
Fish
Shellfish
Tree nuts (eg, walnuts, pecans)
Sesame

Risk Factors

Factors that increase your chance of food allergies include:

Age: young children
History of eczema
History of other types of allergies, including hay fever

Symptoms

Symptoms include:

Gurgling stomach
Stomach cramps, pain
Nausea
Vomiting
Diarrhea
Skin rash, especially hives
Skin itching
Cough
Wheezing
Shortness of breath
Swelling in lips, mouth, tongue, throat
Nasal congestion
Severe drop in blood pressure

Hives

Diagnosis

The doctor will ask about your symptoms and medical history. A physical exam will be done. Food allergies are often diagnosed based on your own observations. It is a good idea to keep a diary of your symptoms. Note when the symptoms occur and what you have eaten.

Tests may include:

Elimination Diet

You may be asked to go on an elimination diet . This should be done under your doctor's care. You will not eat a suspected food. If your symptoms decrease or go away, your doctor can almost always make a diagnosis. If you eat the food and your symptoms come back, the diagnosis is confirmed. This is most often only done in cases of skin irritation or atopic dermatitis . Elimination diets should not be used in cases of severe allergic reaction or anaphylaxis symptoms. These include wheezing, shortness of breath and drop in blood pressure.

Scratch Skin Test

The doctor will dilute an extract of the food. The dilution will be placed on your forearm or back skin. The skin is scratched with a small pick or tiny needles. If there is swelling or redness, an allergic reaction may be present. The doctor will make the diagnosis based on the skin test and your history of symptoms. Some skin tests can have a severe allergic reaction. This test should only be used under the supervision of a physician or other trained medical personnel. Severe eczema may make this test hard to interpret.

RAST or ELISA Test

The doctor may order blood tests (RAST or ELISA). These tests measure the level of food-specific IgE in the blood. IgE is a type of protein that the body produces when it comes in contact with something to which it is allergic. The presence of IgE in the blood may indicate an allergy.

Treatment

Avoid foods and food ingredients that cause you to have an allergic reaction. If you think you've eaten something to which you are allergic, and you have difficulty breathing, call for emergency medical help.

Treatments include:

Antihistamine medication—to decrease swelling and itching
Epinephrine —injected immediately in the event of a severe, life-threatening reaction (anaphylaxis)
Corticosteroid medication—for more severe swelling and itching

If you are diagnosed with a food allergy, follow your doctor's instructions .

Prevention

To reduce your chance of having a food allergy reaction:

Avoid eating or drinking substances to which you know you are allergic.
Read the ingredient label on every food product that you eat.
If you go to a restaurant, discuss your allergy with the food server. Ask about all ingredients.
Learn the other names for all your allergens. This will help you recognize them on an ingredients list.
If you have a severe, anaphylactic-type food allergy, ask your doctor if you should carry a dose of epinephrine with you.
Consider wearing a medical alert bracelet to inform others of your allergy.

RESOURCES:

American Academy of Allergy, Asthma, and Immunology http://www.aaaai.org/
Food Allergy and Anaphylaxis Network http://www.foodallergy.org/

CANADIAN RESOURCES:

Allergy Asthma Information Association http://aaia.ca/
Calgary Allergy Network http://www.calgaryallergy.ca/

References:

Dambro MR, Griffith JA. Griffith's 5-Minute Clinical Consult. Baltimore, MD: Lippincott, Williams, and Wilkins; 1999.
Food allergy: an overview. National Institute of Allergy and Infectious Diseases website. Available at: http://www3.niaid.nih.gov/topics/foodAllergy/PDF/foodallergy.pdf . Published July 2007. Accessed July 7, 2009.
Food Allergy and Anaphylaxis Network website. Available at: http://www.foodallergy.org . Accessed July 7, 2009.
Middleton E. Allergy: Principles and Practice. 5th ed. St. Louis, MO: Mosby-Year Book, Inc.; 1999.

Last reviewed July 2010 by Purvee S. Shah, MD

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