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What is a Food Allergy?

Food allergy describes an abnormal or exaggerated immune system response to a food or substance in a food. Although the allergen is harmless to most people, the allergic individual will have a reaction when the food in question is consumed.

IgE-mediated allergies

The immune system produces several substances that help protect the body, including IgE antibodies. These antibodies are involved in immediate and potentially anaphylactic allergic reactions (severe allergic reactions). When these antibodies come into contact with the food allergen, they can trigger excessive secretion of a substance called histamine, a substance whose inflammatory properties contribute to numerous allergic symptoms. These symptoms will vary from one person to another.

Once a potentially severe reaction is triggered a dose of epinephrine is recommended as soon as possible. This medication works to halt or slow down the cascade of potentially fatal symptoms. People at risk for anaphylaxis should always have their auto-injector handy, as reactions are unpredictable.

Non IgE-mediated allergies

Some people live with other types of food allergies, including allergies not induced by IgE. Symptoms of non IgE-mediated allergies are usually localized in the digestive system and have a slower onset, from a few hours to days following ingestion of the offending food. Symptoms can include projectile vomiting or abnormal stooling patterns (i.e. bloody stool, persistent diarrhea).

Non-IgE mediated allergies include conditions such as food protein-induced enterocolitis syndrome (FPIES), allergic proctocolitis, food protein-induced enteropathy, and celiac disease. Each of these affects the digestive system, but are not considered immune system reactions. In some cases, non IgE-mediated conditions may affect the skin (e.g. allergic contact dermatitis).

Living with dietary restrictions

Regardless of the allergic condition, the affected person must avoid consuming the food that triggers the allergic reaction. Even trace amounts of the allergen can provoke symptoms, so strict avoidance is recommended.

Living with dietary restrictions can be very challenging, considering the prevalence of processed and prepared foods which often contain a long list of ingredients. The allergic individual should read all nutrition labels carefully in order to identify the presence of an allergen. In addition, products labelled as “may contain…”, should be avoided.

Allergic individuals should also avoid cross-contact between foods. This is when an allergen is inadvertently transferred from one food to another, by way of a contaminated surface. Examples of risk for cross contact can include sharing contaminated surfaces (dishes, counters, plates, dishcloths and hands). Several precautions must be taken when purchasing and preparing meals for allergic individuals.