By Dr. Kay Motil
Food allergy, or hypersensitivity, refers to an abnormal immunologic reaction to food.
Allergic reactions to food are caused by IgE activation against specific food proteins or non-IgE activation of other chemical processes involving eosinophil or T-lymphocyte blood cells.
IgE reactions are rapid in onset, beginning within minutes to two hours from the time of food ingestion. Symptoms involve the skin (urticaria, angioedema), respiratory (asthma, allergic rhinitis) or gastrointestinal (vomiting, diarrhea) tracts, and cardiovascular system (anaphylaxis). Non-IgE reactions are chronic and have symptoms isolated to the gastrointestinal tract or skin. Non-IgE food allergy includes protein-induced enterocolitis, eosinophilic enteropathy, celiac disease, and pulmonary hemosiderosis.
Most food allergy is acquired in the first two years of life. The prevalence of food allergy at one year of age is approximately 6-8%, but decreases progressively to 3-4% by late childhood. The prevalence of food allergy has increased over the last 15 years, possibly due to better hygiene.
In young children, 90% of food allergies are caused by cow milk, egg, soy, peanut, wheat, tree nut, fish, and shellfish. In adolescence, the most common food allergies are peanut, tree nut, fish, and shellfish. Most childhood food allergies are lost over time, although the pattern of resolution varies. Allergies to foods other than fish, shellfish, peanuts, and tree nuts usually are outgrown. Recent studies suggest that peanut exposure during pregnancy or early infancy may promote peanut tolerance, but this practice remains controversial.
Parents commonly perceive adverse food reactions, such as perioral rashes, in young children. Cow milk, citrus fruit, strawberry, and tomato account for near two-thirds of all reported reactions under two years of age. The overall duration of the reaction is short, with two-thirds resolved within 6 hours. The explanation for these brief reactions is irritation or non-immunologic reactivity to food.
The prevalence of food allergies in children with ectodermal dysplasia exceeds the occurrence in unaffected children. In a survey conducted by the NFED, parents of 347 children younger than 18 years of age with a diagnosis of an ectodermal dysplasia syndrome or carrier stated completed allergy questionnaires. In the ectodermal dysplasia cohort, 34% had a history of a food reaction to a particular food and 19% had a reaction in the 12 months preceding the survey. Sixteen percent of the ectodermal dysplasia cohort always had a similar reaction after eating a suspected food. The prevalence of physician-diagnosed food allergies in the ED cohort was 21%, including 17% whose condition was diagnosed by blood or skin tests.
The prevalence of food allergies varied among the ectodermal dysplasia syndromes. In the ectodermal dysplasia cohort, 56% with HED, 8% with EEC, 4% with AEC, and 2% with Goltz reported food allergies. Specific foods included: fruits and vegetables, 14%; peanuts, 13%; milk, 10%; egg, 10%; tree nuts, 8%; soy, 4%; shellfish, 4%, and wheat, 3%.
Children should be evaluated by a pediatric allergist when IgE-mediated food allergies are suspected. Skin tests and blood tests are used for the laboratory determination of IgE sensitization to specific foods. Laboratory reactivity is distinct from clinical reactivity. Not all children with laboratory detected IgE food sensitivity have reactions when the food is ingested because gastrointestinal processing alters the antigen. Skin tests are highly sensitive, but only moderately specific, for the diagnosis of food allergy. Blood tests are less sensitive than skin tests.
Non-IgE-mediated food allergies may require an evaluation by a pediatric gastroenterologist. Endoscopic biopsies may be obtained for the laboratory determination of non-IgE disorders.
Non-immunologic reactions to food include gastrointestinal disorders such as lactose intolerance; toxic reactions such as food poisoning; pharmacological intolerances such as caffeine (coffee), tyramine (cheese), serotonin (banana, tomato), or phenylethamine (chocolate); psychological food aversion; and accidental contamination. Allergies to food additives are rare. Migraines are not related to food allergy, although certain foods can trigger headaches due to their chemical properties.
Dietary avoidance of foods to which a child is allergic is the mainstay of food allergy management. Individuals vary with respect to the amount of food that triggers a reaction. Some children who react to specific foods tolerate extensively heated forms of these allergens in small quantities. Children should avoid suspected food allergens, but care should be taken to avoid elimination diets that impose dietary restrictions severe enough to place the child at nutritional risk.
Parents should monitor food allergy in conjunction with their physician. Parents should be certain that food avoidance measures are in place and that reactions are recognized and treated promptly, if appropriate. The allergist may evaluate the child annually by performing blood or skin tests and collecting information on accidental exposures. Supervised food challenges may be performed to prove that the child has outgrown the food allergy.
Allergen avoidance sounds simple, but requires extensive parent education. Parents should know how to read labels on packaged foods, prepare safe meals at home, and avoid food allergens in restaurant meals. Unintended exposures may occur from the use of medications and vaccines, sharing eating utensils, or inadvertent ingestion of cosmetics and children’s crafts. Parents should be prepared to treat an unexpected reaction at all times in any setting.
Kathleen J. Motil, M.D., Ph.D.
Dr. Motil is a research scientist at the USDA/ARS Children’s Nutrition Research Center and an Associate Professor of Pediatrics at Baylor College of Medicine in Houston, Texas. Dr. Motil is the author of many research publications that describe the metabolic relationships between nutrition and growth in children.
Other Posts You Might Like