IgE-mediated food allergies cause your child’s immune system to react abnormally when exposed to one or more specific foods such as milk, egg, wheat and nuts. Children with this type of food allergy will react quickly, within a few minutes to a few hours. Immediate reactions are caused by an allergen-specific immunoglobulin E (IgE) antibody that floats around in the blood stream.
When IgE is working properly, it identifies triggers — such as parasites or other items that could be harmful to the body — and tells the body to release histamine. Histamine causes symptoms such as cough, wheeze and hives.
However, IgE can sometimes react to normal proteins, causing your child’s body to react to a specific food protein or proteins. Once a food is eaten, the protein is absorbed during digestion and enters the bloodstream. That food will cause symptoms throughout the body because of IgE.
For example, if your child has an IgE-mediated allergy to the protein in milk, he may experience symptoms in the skin (hives), stomach (vomiting), lungs (coughing, wheezing), and circulatory system (decreasing blood pressure).
Food allergies are common. Five percent of children under the age of five have a food allergy. Roughly 4 percent of adolescents and adults have a food allergy.
The prevalence of food allergies does seem to be increasing. CHOP researchers are evaluating the genetics of food allergy and possible reasons for the increase in all allergic conditions. Researchers believe many factors may play a role in food allergy development including maternal diet during pregnancy, timing of food introduction, and breastfeeding status.
If you have an “allergic family” — one that includes family members with asthma, environmental allergies and eczema — your child has an increased risk for allergy.
The most common food allergens include:
All of these foods can trigger anaphylaxis (a severe, whole-body allergic reaction) in patients who are allergic.
When your child has a food allergy, her body’s IgE antibodies identify that specific food as an invader and can produce symptoms in multiple areas of the body.
Allergic reactions can be scary, but noticing symptoms early can help your child get proper treatment.
Receiving a diagnosis of food allergy may come in a few ways:
When you meet with allergy specialists at The Children’s Hospital of Philadelphia, we will discuss your child’s food reaction history, as well as get a detailed medical and family history.
Based on your child’s history and findings, our allergy specialists may recommend testing. The gold standard for diagnosing a food allergy is to give the child the suspected trigger food in a controlled setting and monitor the results.
These tests also help determine if your child has outgrown their food allergy.
At CHOP, we perform a “food challenge” to confirm a food allergy or see if a child has outgrown an allergy. A food challenge is performed at the Hospital and the child is given small, increasing amounts of the food of concern over a period of time. The goal is to reach a serving size with no reactions. Learn more about our food challenge.
Your child’s provider may recommend skin testing. Skin-prick testing involves introducing a small quantity of the specific food on your child’s skin, typically on the forearms.
Your child’s arms will be cleaned and marked to identify allergens to be tested. A drop of extract – a liquid form of a specific food protein – is placed on your child’s skin. That drop is touched with a two-pronged needle. The site of the skin testing is then observed for 10-15 minutes. The provider and team will watch for a hive-like bump to appear. The area will be measured and compared with the positive (histamine) and negative (water) control.
Your child's doctor will monitor the skin test size over time, and if small enough, may recommend an oral food challenge to see if your child is truly allergic. There is a chance for false positives with skin testing.
If the skin test reaction to a particular food is large enough, and the child has had a history of reactions to that food, a diagnosis of IgE-mediated food allergy is likely.
Intradermal testing — injecting a small amount of the suspected allergen under the surface of the skin — is not recommended for foods.
Another useful tool in diagnosing and managing food allergies is blood testing, called allergen-specific IgE testing. This test measures the level of antibody produced in the blood in response to a food allergen. The level of specific IgE to a food in the blood (previously known as RAST testing) does not describe the severity of the reaction if a food is consumed.
This is a useful tool your allergist may use to measure trends in blood work, in addition to skin testing and reaction history. The blood test should not be done on foods that are currently being consumed.
There is also a newer type of blood test, known as component testing, which may help to identify true allergens compared to false positives.
Reactions to food can be different every time. Your child’s reaction can depend on a variety of factors including:
In addition, the way the food was prepared and the amount of food protein ingested can affect your child’s reaction.
Allergic reactions can occur quickly, so whenever more than one body system is involved in a food reaction (i.e. throat and skin); the best treatment available is Epinephrine. Epinephrine comes in a variety of forms including auto-injectors, such as Epi-Pen, Auvi-Q and other generic forms.
If your child’s reaction is mild at first — and you’ve given him an antihistamine — then the reaction quickly worsens, you should give epinephrine.
Children with food allergies should always carry epinephrine with them, or it should be readily available at places where they routinely spend time such as school, daycare and home.
If your child is experiencing a severe allergic reaction – whether you gave him epinephrine or not – you should call 911. This is because your child has experienced a significant allergic reaction, not because of the epinephrine. This drug works well, but wears off quickly. Your child should be evaluated by medical personnel.
If a reaction is getting worse, your child may be given other medicines such as:
Some children with IgE-mediated food allergies will outgrow their sensitivity. For example, we know that milk, egg and soy allergies are more commonly outgrown during childhood and adolescence; while peanut and tree nut allergies are more likely to persist. Only about 20 percent of patients with peanut and tree nut allergies will outgrow them.
Not all children outgrow their allergies. Certain factors have been associated with the persistence of food allergies, including:
The majority of children with an egg allergy are able to tolerate cooked eggs as part of another food, such as cake (about two eggs per cake, heated at 350 degrees and cooked for 30 minutes). These same children typically would not tolerate a lightly heated egg, such as scrambled eggs or as part of French toast.
Similarly, many children with a milk allergy are able to tolerate small amounts of heated milk in other food products.
If your child is able to tolerate these heated forms, there is a better chance of outgrowing his food allergen. Speak with your allergist about a food challenge to the baked form of egg and milk.
If your child is not able to tolerate the heated form of these foods, it is more likely she will have an IgE-mediated food allergy throughout their lives.
The Children’s Hospital of Philadelphia and other centers are actively involved in researching the causes of and treatments for food allergies. Oral and skin desensitization studies are underway in the United States.
If you are interested in participating in a research study, contact CHOP’s Allergy and Immunology Department at 215-590-2549 to be placed on the waiting list. Lottery-based systems are used to select participants.
Reviewed by: Megan T. Ott, MSN, RN, CPNP, and Jonathan Spergel, MD, PhD
Date: January 2014