Food Allergy Myths and Facts
Dean allergist Dr. Reid Olson explains four common misconceptions about food allergies
Myth 1: All food-related adverse reactions are due to an "allergy."
Fact: Food allergy is often confused with food intolerance. The primary difference is that food allergy is specific, reproducible, rapid in onset, and most importantly, potentially life-threatening.
Food intolerance is more commonly defined as unpleasant symptoms that primarily involve the digestive tract. Symptoms may include stomach upset, bloating, cramps, nausea, vomiting diarrhea or constipation. A prime example of this is lactose intolerance which is due to the inability to convert lactose into glucose.
Food allergy is a specific immune response usually involving IgE that occurs reproducibly on exposure to a given food. The prevalence is perhaps three to eight percent of children and less than two percent of adults. This is far less than reported food intolerance which can occur in up to 30 percent of the population. There seems to be an increasing prevalence of food allergy, particularly to peanuts and tree nuts,in children over the past decade. Unfortunately, the factors responsible for this are unknown.
The most common food allergens in the United States are:
- Tree nuts
This is usually due to specific proteins found in these foods.
Myth 2: If a person is allergic to shellfish they are allergic to iodine.
Fact: There is no relationship between the shellfish allergen, which is a muscle protein, and iodine. A person allergic to shellfish has no increased risk of reacting to X-Ray contrast involving iodine compounds.
Upon exposure, symptoms usually start rapidly but occasionally may take up to two hours to develop. Symptoms of food allergy can include nausea, abdominal pain and vomiting, skin rashes and itching, wheezing, cough or chest tightness, nasal congestion, throat swelling or hoarseness. The most feared response to food allergens is anaphylaxis which involves widespread massive release of allergic chemicals and can be rapid in onset and potentially fatal.
Myth 3: With each exposure to a food allergen, the reaction is likely to get worse.
Fact: Although a reaction is likely to occur in a patient who is exposed to a food that they are allergic to, the severity can be highly variable and unpredictable! It may depend on whether the allergen was ingested, inhaled or contacted a skin area. Risk factors for more severe reactions may include a history of asthma, alcohol use and/or concomitant exercise.
Food allergy most commonly presents in childhood during the first few years of life, but allergy to shellfish or fish may develop in adulthood. Allergy to milk, egg, wheat and soy may often be outgrown, while sensitivity to peanuts or tree nuts often persist. Children allergic to egg, wheat, milk or soy may first be able to tolerate these foods if they are first heated such as in baking or cooking with the food.
Like most everything else in the medical field, the diagnosis of food allergy starts with a careful history. This should include: a list of the possible foods suspected, the route of exposure (oral , ingested or topical), the timing of the onset of symptoms after exposure and details of the specific symptoms and their severity. It is also important to note if this has happened more than once when in contact with the suspected food.
Skin prick testing is one of the more common methods used to aid the diagnosis of a specific food allergy. This is done by placing a small drop of the food extract or material on the skin - and making a tiny puncture. Results can be determined within 15 minutes and are dependent on the size of the wheal and flare response. Caution is necessary since very sensitive patients may experience a systemic allergic reaction to testing.
Food allergy testing can also be done by obtaining a sample of blood but are more expensive and may take several days for the results to become available. Double blind, placebo controlled oral food challenges are the most specific means to diagnose food allergy. However, this is rather time and labor intensive and should be done only if the history or specific food testing is equivocal or questionable.
Once a diagnosis of a specific food allergy is made, the primary therapy is strict avoidance of that food or foods. Patients, their families or other caregivers need to be educated on how to read food labels and how to ask whether prepared foods might contain the allergen. Younger children should be taught to never share food from someone else, unless it is from a trusted source. All patients should have self-injectable epinephrine always available and should have a medical alert bracelet or tag they can wear.
Myth 4: Allergic reactions to food can safely be treated with antihistamines such as Benadryl.
Fact: Epinephrine is always the drug of choice to treat an allergic emergency. Epinephrine works quickly and can stop an allergic response more completely than antihistamines such as Benadryl. Fatalities due to severe food allergy are more common when there is a delay in the administration of epinephrine or a false reliance on antihistamines.
There is currently no other approved treatment for food allergy other than careful avoidance, although there is promise of better therapy in the future. It remains unclear whether restricting the mother’s diet during pregnancy or breast feeding affects the development of food allergy in their children. Breast feeding for at least four to six months after birth is most commonly recommended.
Although food allergy can be serious, understanding and careful planning can greatly minimize any risks and allow patients to live a normal and nutritional sound life. Please feel free to contact the Dean Clinic Allergy department for advice or questions.