Clinical Reference Systems: Pediatric Advisor 10.0
Spanish version

THE CHARACTERISTICS OF FOOD ALLERGIES

Food allergies tend to be overdiagnosed, but about 5% of children have true allergic reactions to food. Suspect that 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:

The most common reactions are:

• 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, or sudden fall in blood pressure (shock).

Children who have other allergic conditions, such as eczema, asthma, or hay fever are more likely to have associated food allergies than children who do not have 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 typical symptoms of food allergies listed above. Attention deficit disorder and behavioral disorders, as isolated symptoms, 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.

THE CAUSE OF FOOD ALLERGIES

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 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.

FOODS THAT OFTEN CAUSE ALLERGIES

Overall, the food that most often causes allergies is the peanut. In infants, 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.

OUTGROWING FOOD ALLERGIES

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) are more often outgrown than others. Although 3% to 4% of all infants have a cow's milk allergy, less than 1% of these infants are allergic to milk the rest of their lives. Allergies to tree nuts, peanuts, fish, and shellfish (shrimp, crab, and lobster) often do last a lifetime.

DIAGNOSING A FOOD ALLERGY

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. There may be some inconsistency because the 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 consumed. Call your child's physician before you rechallenge.

TREATMENT OF FOOD ALLERGIES

1. Your child should 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.

2. 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.

3. If hives or itching are the only symptoms, give Benadryl four times a day until the hives are gone for 12 hours.

4. Provide a substitute for any missing vitamins or minerals.

   Eliminating single foods from the diet usually does not cause any dietary 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 physician or a nutritionist about dietary supplements (such as vitamins).

5. Your child should try eating the food again in about 3 to 6 months. (CAUTION: Never do this if a child has had a severe or anaphylactic reaction to a food. Such a child should avoid that food for the rest of his life. You should also keep emergency kits with epinephrine-loaded syringes at home, at school, and in the car).

   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.

PREVENTING FOOD ALLERGIES IN HIGH-RISK CHILDREN

Children are more likely to have allergies if they have parents, brothers, or sisters with asthma, eczema, severe hay fever, or food allergies. The risk is highest if both parents are allergic to foods.

The onset of allergies in these children may be delayed if you are careful about their diet. If possible, they should breast-feed until they are at least 1 year old. The mother should avoid eating or drinking milk products, peanuts, and eggs during this time. If the mother cannot breast-feed during the first year, she 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 TO CALL

1. CALL AN EMERGENCY RESCUE SQUAD (911) IMMEDIATELY IF:
   • Your child develops any serious symptoms, such as wheezing, croupy cough, difficulty breathing, passing out, or tightness in the chest or throat.

2. CALL YOUR CHILD'S PHYSICIAN 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.

RECOMMENDED READING

FOOD ALLERGY: A Primer for People; by S. Allan Bock; Vantage Press, 1988.

The Food Allergy Network (8-page newsletter of practical tips published six times a year), 10400 Eaton Place, Suite 107, Fairfax, VA 22030; 800-929-4040; www.foodallergy.org.