A food allergy is a reaction by the body that happens when the immune system mistakenly identifies an ingredient in a food, most frequently a protein, as an “enemy” and develops a response against it.  Typically, this response is mediated by specific antibodies (called specific IgE antibodies), and an immediate reaction (seconds to minutes) occurs when these antibodies identify the “enemy” protein.  Diagnosis of a food allergy relies primarily on a history of having a reaction to a food, but certain kinds of testing (blood tests and skin tests) may help confirm the suspicion of a reaction.

Food allergies are different from food intolerance, which is a response from the digestive system, not the immune system. Typically, the properties of certain foods may cause an unpleasant irritation of the digestive system, possibly due to difficulty digesting certain parts of the foods. Lactose intolerance is a common food intolerance that occurs when the digestive system does not have enough of an enzyme to help the body break down a sugar (lactose), which then gets turned into gas by bacteria in the gut.  This can cause abdominal discomfort, such as bloating, gas, or diarrhea. Other foods that may have different properties or side effects may also cause symptoms that are not immune related. These might be things such as caffeine from coffee causing jitteriness, or fiber from prunes leading to looser stools.

Food Allergies

By Dennis Clements, MD, PhD

Your child breaks out in a red, itchy rash after eating at a restaurant. Questions jump to your mind: Does she have a food allergy? How should I treat it – with antihistamine or epinephrine? Is this something I need to worry about for the rest of her life?

Many parents ask me if their child could be allergic to foods. Often they ask when someone in the family is said to have a food allergy or they know someone with a food allergy.

For this month’s column, I asked Dr. Wesley Burks, Professor and Former Chief of the Division of Pediatric Allergy and Immunology at Duke University, to make sense of food allergy and help us understand how we test for and treat pediatric food allergies.

--Dennis Clements, MD, PhD

Food allergy occurs in 4 to 6 percent of young children and 3 to 4 percent of adults. It can be a major cause of life-threatening allergic reactions.

Milk, egg, and peanuts are the most common foods that cause food allergy, followed by wheat, soy, fish, shellfish, and tree nuts such as walnuts and pecans. Other foods may cause allergic reactions but much less commonly.

Reactions to peanuts, which cause the most reactions, can range from simple hives to severe systemic reactions. Almost 1 percent of young children in the United States are thought to be allergic to peanuts. In the last 15 years the number of children who have peanut allergy has doubled for reasons that are not entirely clear.

Testing for Food Allergies

The diagnosis of peanut and other food allergies is made by taking a careful clinical history from the patient and family. Generally, allergic reactions happen within seconds to minutes after eating the food. The symptoms are reproducible, which means that each time the food is eaten the same general symptoms occur.

Normally, foods need to be eaten -- not just inhaled or touched -- to cause any serious allergic reactions. Often the physician making the diagnosis will then look for the allergic protein to the food (called IgE) using skin scratch testing or blood testing.

A negative test is a good sign that the child is not allergic to the food, while a positive test only indicates the child may be allergic to that food.

Treatment of Food Allergies

After the diagnosis, the treatment for food allergy is elimination of the food from the diet. This sounds easier than it really is for the patient and family. Compliance with an elimination diet is time-consuming, inconvenient, and requires a great deal of education and commitment on the part of the patient and all caregivers.

The Food Allergy and Anaphylaxis Network, a non-profit patient advocacy group, is an invaluable resource for parents as well as physicians in this endeavor. Even with good educational information, about half of food-allergic patients have accidental ingestions and subsequent allergic reactions after diagnosis.

Incorrect or difficult-to-read food labels may result in accidental ingestion of the food. The United States Food and Drug Administration requires food manufacturers to declare all food ingredients on food labels. However, some of the wording does not clearly indicate the presence of a food allergen. For instance, “natural flavorings” may contain several individual ingredients including whey, or “vegetable proteins” may include soybean.

The Food Allergen Labeling and Consumer Protection Act (FALCPA), which takes effect January 1, 2006, will address some of the limitations of current food labeling practices. FALCPA requires food manufacturers to plainly state the presence of the eight major food allergens: milk, egg, wheat, soybean, peanut, tree nuts, fish, and shellfish.

Managing Acute Reactions

Because accidental food ingestions can not always be avoided, patients and their caregivers must be equipped to manage acute food-induced reactions. Individualized treatment plans should be prepared in advance and medications readily available. These medications may include antihistamines (Benadryl, for example) and injectable epinephrine (Epipen).

The food allergies to milk, egg, wheat, and soybean are generally expected to be outgrown by about school age, while other food allergies -- like peanut, tree nuts, fish, and shellfish -- are likely to be with a person for life.

A number of research studies are ongoing at Duke and nationally that will likely change the treatment of peanut and other food allergies in the next several years.

These novel forms of treatment for food allergy hold promise for the safe and effective treatment of food-allergic individuals and the prevention of food allergy in the future. It is likely that some type of allergy immunotherapy (or “vaccine”) for food allergy will be available relatively soon. Then perhaps these food allergy worries can be a fear of the past.

Dennis Clements, MD, PhD, is the Chief of Primary Care Pediatrics at Duke Children's Hospital.