IgE-Mediated Food Allergies
What are IgE-mediated food allergies?
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 or 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.
The most common food allergens include:
- Tree nuts
All of these foods can trigger anaphylaxis (a severe, whole-body allergic reaction) in patients who are allergic.
Food allergies are common: 5 percent of children under the age of five have a food allergy and roughly 4 percent of adolescents and adults have a food allergy.
The prevalence of food allergies does seem to be increasing. Researchers at The Children's Hospital of Philadelphia 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.
Causes of IgE-mediated food allergies
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).
Signs and symptoms of IgE-mediated food allergies
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, including:
- Skin: “hives” (red blotches or welts that itch), mild to severe swelling
- Eyes: tearing, redness, itch
- Nose: clear discharge, itch, congestion
- Mouth: itch, lip swelling, tongue swelling
- Throat: tightness, trouble speaking, trouble inhaling
- Lungs: shortness of breath, rapid breathing, cough, wheeze
- Stomach: repeated vomiting, nausea, abdominal pain, diarrhea (usually later)
- Heart and circulation: weak pulse, loss of consciousness
- Brain: anxiety, agitation, loss of consciousness
Allergic reactions can be scary, but noticing symptoms early can help your child get proper treatment.
Reactions to food can be different every time. Your child’s reaction can depend on a variety of factors including the amount of food eaten, uncontrolled asthma, and illness. In addition, the way the food was prepared and the amount of food protein ingested can affect your child’s reaction.
Testing and diagnosis of IgE-mediated food allergies
Diagnosing food allergies can happen a few ways:
- Your child may have had a reaction to a food which led to an evaluation by an allergist
- Your child may have had a flare of eczema, which led to concerns about a food allergy
- You may have discussed concerns about your child with her pediatrician, who recommended consultation with a specialist
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. This is called a food challenge test and it can also help determine if your child has outgrown a food allergy.
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.
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.
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.
Treatments for IgE-mediated food allergies
Allergic reactions can occur quickly. 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.
When to call 911
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 need other medicines such as:
- Antihistamines (such as Diphenhydramine and Cetirizine)
- Albuterol, a bronchodilator inhaler used for breathing issues
- Medications to reduce stomach acid, such as Ranitidine
Outlook for IgE-mediated food allergies
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.
Certain factors have been associated with the persistence of food allergies, including:
- Age of first allergic reaction
- Severity of allergic reaction
- Whether the child has asthma
- History of eczema
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.
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.