A food allergy is an abnormal and disproportionate reaction of the immune system to the ingestion of a food.

Food allergies are common (affecting 1 to 6% of the population) and can affect many foods: peanuts (peanuts), nuts, fish, shellfish, but also wheat, cow’s milk protein, soy, egg, fruit exotic, etc. In total, more than 70 foods are considered allergens potential.

Symptoms vary in severity. They range from temporary discomfort (tearing, irritation, gastrointestinal upset) to serious reactions that can be fatal, which require immediate medical intervention.

In Europe and North America, peanuts and walnuts, hazelnuts, almonds are the foods most often involved in serious reactions which are life-threatening.

The allergic reactions usually occur within a few minutes or an hour of ingestion of the offending food.

It is not always easy to identify with certainty a food to which you are allergic. In addition, there may be cross allergies (eg nuts and almonds) and it is important to do tests to find out which foods are problematic, especially in children.

There are several tests to diagnose a food allergy. The allergic “investigation” always begins with an interview with a allergist who inquires about the symptoms felt and their history.

It is then possible to perform:

• of the prick-tests cutaneous : they consist in bringing cells of the dermis into contact with the supposed allergen. These skin tests consist in placing a drop of allergen on the skin and then making a small puncture through the drop of reagent, to make it penetrate into the dermis. The tests are carried out on the arm or the back. You can do several at the same time. Ten to fifteen minutes later, we assess the size of the edema (or redness) that has formed if there is indeed an allergy.
• un serum IgE assay : a blood test allows to look for the presence of a certain type of immunoglobulins, the IgE, characteristics of the allergic reaction. We look for the presence of IgE specific to the tested allergen. It is not necessary to be on an empty stomach to perform this dosage.
• of the patch tests (or patch tests): they can be useful in certain cases of allergies, for example for digestive or skin symptoms. They consist in keeping the allergen in contact with the skin thanks to a self-adhesive device which must not be wet or removed before reading the result 48 to 96 hours later. These patches are often placed on the upper back.

When one or more tests cited above reveal the existence of a food allergy, the doctor will advise an exclusion diet aimed at banishing all foods, processed or not, which contain the allergen. This is the only way to avoid allergic reactions.

He will also prescribe anti-allergy drugs in the event of accidental consumption, especially if the reaction is severe (antihistamine, corticosteroids or adrenaline in a self-injectable syringe – Epipen in Quebec, Anapen in France).

Most often, the allergy will be confirmed by an oral challenge test, which involves administering the allergen in the hospital, under control, in gradually increasing doses, every 20 minutes until the reaction occurs. This test makes it possible to know the quantity of food which causes the symptoms and to better define the type of symptoms.