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Food Allergies

What are food allergies?

A food allergy is when the body's immune system reacts as if a certain food is harmful. Food allergies tend to be overdiagnosed, but about 5% of children have true allergic reactions to food. Your child may have a food allergy if he or she has any of the following allergic symptoms within 2 hours after eating certain foods:

  • lips, tongue, or mouth swelling
  • diarrhea or vomiting
  • hives
  • itchy red skin (especially if a child already has eczema).

Some less common symptoms are:

  • sore throat or throat clearing
  • nasal congestion, runny nose, sneezing, or sniffing (especially if a child has hay fever).

Rarely a child has a severe allergic reaction (called an "anaphylactic reaction") that may be life-threatening. Symptoms of such a reaction are a sudden difficulty breathing, sudden difficulty swallowing, weakness from a sudden fall in blood pressure (shock), or confused thinking.

Children who have other allergic conditions, such as eczema, asthma, or hay fever are more likely to have food allergies than children who do not have other allergies. A few children who have asthma, migraine headaches, colic, or recurrent abdominal pain may have attacks of these problems triggered by food allergies. If an attack is triggered by a food allergy the child will also have some of the symptoms of food allergies listed above. Attention deficit disorder and behavioral disorders have not been scientifically linked to food allergies.

If other family members (parents or brothers or sisters) have food allergies, a child has a greater chance of also having a food allergy. Food allergies are often inherited.

What is the cause?

Allergic children produce antibodies against certain foods. When these antibodies come in contact with the food that causes the allergy, there is a reaction between the antibodies and the food. This reaction releases chemicals (such as histamines) that cause the allergy symptoms.

The tendency to be allergic is inherited. If one parent has allergies, each child has about a 40% chance of developing allergies. If both parents have allergies, the chance of food allergy rises to about 75% for each child. Sometimes a child is allergic to the same food(s) as the parent.

What are the most common food allergies?

Overall, the food that most often causes allergies is the peanut. In babies, allergies to eggs and milk products are more common. Peanuts (and peanut butter), eggs, cow's milk products, soybeans (and soy formula), and wheat cause over 80% of food reactions. These foods plus fish, shellfish, and tree nuts cause over 95% of all food reactions. Chocolate, strawberries, corn, and tomatoes are often blamed for allergic reactions, but actually these foods rarely cause allergic reactions.

Will my child outgrow a food allergy?

At least half of the children who develop a food allergy during the first year of life outgrow it by the time they are 2 or 3 years old. Some reactions to food (for example, milk or soy) are more often outgrown than others. Although 3% to 4% of all babies have a cow's milk allergy, less than 1% of them are allergic to milk for the rest of their lives. Allergies to tree nuts, peanuts, fish, and shellfish (shrimp, crab, and lobster) often do last a lifetime.

How is it diagnosed?

Take the following steps to determine whether your child has a food allergy and what foods cause the allergy.

  1. Keep a diary of symptoms and recently eaten foods.

    If you already know what food is causing an allergic reaction, go directly to step 2. Otherwise, be a good detective and keep a diary of foods and symptoms for 2 weeks. Any time your child has symptoms, write down the foods that he or she ate during the last meal.

    After 2 weeks, look at the diary to see if your child ate any of the same foods on the days he or she had symptoms. Symptoms may depend on how much of the food your child ate. Anaphylactic reactions can be triggered by even small amounts of foods, but other allergic symptoms (for example, diarrhea) and their degree of severity usually depend on how much of the food your child eats.

    Reactions to food may be worse when a child is also reacting to other substances in the environment, such as pollens (hay fever). Therefore, food allergies may flare up during pollen season.

  2. Have your child stop eating the suspected food for 2 weeks.

    Record in the diary any symptoms that your child has during this time. If you have eliminated the correct food from the diet, your child should stop having allergic symptoms. Most children improve within 2 days. Almost all of them improve after 1 week of not eating the food causing the allergy.

  3. Have your child start eating the suspected food again. (CAUTION: Never do this if your child has had a severe or anaphylactic reaction to a food).

    This is called "rechallenging" and the purpose is to prove that the suspected food is definitely the cause of your child's symptoms. Give your child a small amount of the food you think is causing the allergy. The same allergic symptoms should appear within 10 minutes to 2 hours after the food is eaten. Call your child's health care provider before you rechallenge.

Skin prick tests or a blood test may also be used to help figure out what food your child is allergic to.

How is it treated?

  • Avoid eating the food that causes the allergy.

    This should keep your child free of symptoms. If your child is breast-feeding and is allergic to a food that you are eating, do not eat this food until your child stops breast-feeding. Food allergens can be absorbed from your diet and enter the breast milk. Talk to a nutritionist if you have questions.

  • Consider avoiding other foods in the same food group.

    Some children are allergic to two or more foods. Occasionally the foods belong to the same food group. This happens most often to children who are allergic to ragweed pollen. These children often react to watermelon, cantaloupe, muskmelon, honeydew melon, and other foods in the gourd family. Children allergic to peanuts may react to soybeans, peas, or other beans. Most nuts from trees are not related to each other. For example, a child who is allergic to walnuts will probably not be allergic to other tree nuts.

  • If hives or itching are the only symptoms, give Benadryl 4 times a day until the hives are gone for 12 hours.
  • Join the Food Allergy and Anaphylaxis Network.

    This national organization can help with any food allergy questions you might have. Contact them at 800-929-4040 or

  • Provide a substitute for any missing vitamins or minerals.

    Eliminating single foods from the diet usually does not cause any nutrition problems. However, if you eliminate a major food group, you will need to make sure your child gets all the nutrients he or she needs from other sources. For example, if you eliminate dairy products, your child will need to get calcium and vitamin D from other foods or supplements. Talk to your health care provider or a nutritionist about dietary supplements (such as vitamins).

  • For mild reactions, your child can try the food again in about 6 months.

    Many food allergies are temporary. If a child is less than 3 years old, he or she should try eating the food every 6 months until the age of 3. If the child continues to react to the food each time, get an evaluation by a board-certified allergist before you permanently eliminate the food from the diet. CAUTION: Never let your child try the food again if he or she had a severe or anaphylactic reaction to it. In these cases, the food should be avoided for the rest of his or her life. You should also keep emergency kits with epinephrine-loaded syringes at home, at school, and in the car.

How can I help prevent food allergies?

If food allergies run in your family, you may be able to delay the onset of the allergies if you are careful about your child's diet. If possible, breast-feed your baby until they are at least 1 year old. The breast-feeding mother should avoid eating or drinking milk products, peanuts, and eggs during this time. If you cannot breast-feed during the first year, you should use either a formula made from protein hydrolysate (called an "elemental formula") or a soy protein formula.

The allergy-prone child should not have any solid foods until the age of 6 months. Try to avoid milk products, eggs, peanut butter, soy protein, fish, wheat, and citrus fruits in the child's diet during the entire first year of life. Try to avoid peanuts and fish until age 2 years.

When should I call my child's health care provider?

Call 911 IMMEDIATELY if:

  • Your child develops any serious symptoms, such as wheezing, croupy, barky cough, trouble breathing, passing out, or tightness in the chest or throat.

Call during office hours if:

  • You suspect your child has a food allergy.
  • You want to rechallenge your child with a food you think your child is allergic to.
  • You have other questions or concerns.
Written by B.D. Schmitt, M.D., author of "Your Child's Health," Bantam Books.
Published by McKesson Provider Technologies.
Last modified: 2006-05-23
Last reviewed: 2006-02-23
This content is reviewed periodically and is subject to change as new health information becomes available. The information is intended to inform and educate and is not a replacement for medical evaluation, advice, diagnosis or treatment by a healthcare professional.
Copyright 2006 McKesson Corporation and/or one of its subsidiaries. All Rights Reserved.
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