Food allergies occur when the immune system mistakenly attacks a food protein. The body creates proteins called antibodies (IgE) that bind to the protein of the particular food to which one is allergic, peanut, for example. Ingestion of the offending food will trigger IgE to bind to that food protein and cause the sudden release of chemicals, including histamine, resulting in symptoms of an allergic reaction. The symptoms may be mild (rashes, hives, itching, swelling, etc.) or severe (trouble breathing, wheezing, loss of consciousness, etc.). A food allergy can be fatal.
Food allergies are a growing concern, especially when it is a child who is affected. The prevalence is highest in the first 2 years of life with a peak of 6-8% in one year olds. The prevalence falls progressively with time to an average of 3% of the total population. Food allergy does occur in adults, but it is much less common than in children. Many parents will report an adverse reaction to foods that are not true allergies. These can include a transient rash around the mouth from strawberries, tomato products, and citrus as well as lactose or milk intolerance.
In children, the most common food allergens are milk, egg, wheat, soy, peanuts and nuts. Adults who develop food allergies are more likely to be allergic to peanut, tree nut and seafood, especially shrimp. Children can also develop allergies to shellfish and fish. Eighty percent of children with egg or milk allergy will outgrow these sensitivities by puberty. Unfortunately, only about 25% of patients lose their sensitivity for peanut allergy, however. Very few adults who develop allergy to tree nuts, peanuts or seafood become tolerant.
What Happens to Food Allergies Over Time?
Food allergy is often an early indicator that other allergies may follow. Children with food allergy, especially to eggs, have a 50-90% chance of developing allergies and asthma as they get older. Of milk allergic children, 50% will have an allergy to other foods and 40% of children with peanut allergy will develop allergy to other nuts. Some children with eczema may have an allergy trigger.
Symptoms of Food Allergy
Reactions to foods can vary. Symptoms include urticaria (hives), angioedema (swelling), throat clearing, wheezing, vomiting, cramping, diarrhea, hypotension (low blood pressure) and death. Of the reported cases of near fatal and fatal anaphylaxis to peanut, delay in the use of injectable epinephrine was the number one cause for the fatal outcome. It is critical that patients with food allergy carry injectable epinephrine. They need to be taught in the allergist’s office how to use it correctly. Since delayed reactions can occur, patients who use their epinephrine should proceed to their local emergency room for observation.
The Importance of Diagnosing Food Allergy
Allergy skin testing is the most accurate and preferred method of evaluating allergies. These tests are safe, minimally invasive, and easily interpreted. Blood assays or RAST may present the clinician with diagnostic challenges. Studies have shown variability between different labs so that results can be difficult to interpret. Blood tests also have decreased sensitivity compared to skin testing. Results from blood tests can often take a week or longer to be reported.
There are times when an oral food challenge is performed to confirm or reject a specific food allergy diagnosis. It is very important for a patient suspecting a food allergy be treated by a certified allergy specialist.
The most important aspect of treatment is an accurate diagnosis of food allergy. There is no cure for food allergy at this time. Strict avoidance of the allergy-causing food is the ONLY way to prevent a reaction. Every patient should read labels on packaged foods and ask friends and family what ingredients they have used. Do not eat foods from a buffet that you cannot identify and do not be shy in restaurants. Always make the chef aware of your specific allergies.
Always be prepared for accidental ingestion by carrying self-injectable epinephrine. There are currently two forms of auto-injectable epinephrine: Epi-Pen and Auvi-Q. Make sure you are trained and comfortable with how to use the one you have.
Oral Food Allergy Syndrome- oral reactions to certain fresh fruits
Many patients with pollen allergy specifically to trees and weeds experience mouth and throat itching when eating some fresh fruits and vegetables. For example, a patient who is allergic to tree pollen may experience mouth itching when eating apples. Patients with ragweed allergy may experience mouth itching from eating melons and bananas. Oral allergy syndrome reactions may be mild or moderate but never severe. It is important to tell your allergist if you experience any of these symptoms.
The Food Allergy & Anaphylaxis Network is a website for information about food allergies. Visit their web site at www.foodallergy.org.