Food allergy
True food allergy involves an interaction between the body's immune system and the protein in a particular food. The allergy antibody involved in the most common type of food allergy is called immunoglobulin E (IgE). It is important to distinguish food allergy from other non-immune reactions because IgE-mediated allergy can lead to severe or potentially fatal reactions called anaphylaxis. This is why you may hear food allergy referred to as anaphylactic food allergy.
Food allergies are most common in the first 3 years of life; approximately 6% of U.S. children have them. The latest studies estimate that 4% of the U.S. population in all age groups has food allergies. The vast majority of food allergy reactions are caused by a relatively small number of foods. These foods are cow's milk, egg, soy, wheat, peanut, tree nuts, fish, and shellfish. In children, the most common food allergy is to cow's milk followed by egg and peanut. In adults, the majority of reactions are caused by peanut, tree nuts, fish, and shellfish. Food allergy appears to be increasing in prevalence. For example, peanut allergy in the U.S. doubled in young children between 1997 and 2002.
Who is at risk?
Allergic diseases, such as asthma, allergic rhinitis (hay fever), atopic dermatitis (eczema), and food allergy, tend to run in families. Sometimes, however, no obvious family history of allergy is found.
What are the symptoms of IgE-mediated food allergy?
Symptoms usually occur within two hours of eating the allergenic food. After the initial reaction, symptoms will return each and every time the food is ingested. Common symptoms include hives (a raised, "welty," itchy rash), swelling around the eyes or of the lips, forceful vomiting, coughing, choking, or wheezing. A severe reaction called anaphylaxis may be life-threatening. Anaphylactic reactions are systemic (involving the entire body) and can involve:
- The mouth and throat, causing tongue swelling, throat tightness, choking or hoarse voice
- The lungs, causing cough, wheeze or difficulty breathing
- The heart, causing a drop in blood pressure or loss of consciousness.
Some food allergy reactions are biphasic. This means the person has a "second" reaction that occurs 2 to 6 hours after the first reaction. Therefore, a period of monitoring in a medical setting (such as an emergency department) is required after an anaphylactic reaction.
Eczema or atopic dermatitis may be the initial sign of food allergy, particularly in young infants with moderate to severe skin lesions that are not responsive to topical steroids. Appropriate dry skin care and a trial of treatment with topical steroids are necessary before looking for food allergy.