Allergies , food intolerances, hyper-reactivity , provoking agent, allergen, atopy, hypersensitivity, E immunoglobulins, IgE, immunological, lactose intolerance, shortage, defence reaction, sensitisation, intruder, lack of enzymatic production, immuno-allergic mechanism, allergic reaction

Allergies and food intolerances

The definition of allergies introduces the notions of hyper-reactivity of the allergic person and specific nature of the provoking agent or "allergen". This is defined as any substance capable of sensitising the organism of certain individuals and determining pathological manifestations when reintroduced.

The term "atopy" characterises the hereditary predisposition to be sensitive to certain environmental substances based on an early hypersensitivity mechanism mediated by E immunoglobulins (IgE). It is, however, possible to be atopic without developing allergic reactions.

Even though an allergy doesn't always depend solely on the presence of IgE, the allergic reaction is always immunological, unlike what happens for "food intolerances" (generally associated with a lack of enzymatic production) which clinically imitate allergic reactions but do not strictly speaking respond to an immuno-allergic mechanism.

The classic example of food intolerance is lactose intolerance due to a shortage of the enzyme lactase. This is the clinical translation of the disappearance of the ability to digest lactose, the main sugar in milk. This very common illness manifests itself through abdominal pains and diarrhoea after consuming milk.

"True" food allergy corresponds to clinical manifestations appearing after consumption of a food allergen. Allergens do not pose a danger to the organism per se, unlike bacteria, viruses or parasites, but the immune system of certain people wrongly considers them as hazards and triggers a defence reaction against the intruder which is the cause of the clinical symptomatology.

The mechanism of the type I IgE dependent immediate allergic reaction (the most common mechanism) usually occurs in 2 stages

First stage: sensitisation
On first contact of the allergen with the immune system, specific IgEs are produced which then spread throughout the body in the bloodstream and attach themselves to target cells in the skin and mucous membranes (mastocytes) and to circulating target cells (basophil granulocytes). This first stage, called the sensitisation stage, which is clinically silent, prepares the body for an immediate reaction on second contact with the allergen.

Second stage: the actual allergic reaction
On second contact with the allergen (or an allergen of similar structure in the event of cross allergies), the bridging of specific membrane IgEs produced during the active mastocyte and basophil stage releases chemical mediators. It is this release of mediators (the main one being histamine) that is responsible for clinical manifestations of an allergic nature and varying degrees of severity depending on the individual.

Prevalence of food allergies

In France, the prevalence of progressive food allergies in the general population is around 3.2%.
Although food allergies can surface at any age, they remain more common in children; indeed, the prevalence of food allergies in children is around 6 and 8%. The symptomatology may disappear with age, depending on the type of food.

The most commonly identified allergens in children, in France, are eggs (34% of cases) followed by peanuts (25% of cases), milk (8%) and fish (5%). The vast majority are food allergens of animal origin, peanuts and other nuts (Source CICBAA).

The most commonly identified allergens in adults, however, are of plant origin: fruits from the latex group (bananas, avocados, chestnuts, kiwis, etc.) account for up to 14% of cases, followed by rosaceous fruits (apricots, cherries, strawberries, raspberries, hazelnuts, peaches, pears, apples, plums) which account for 13% of allergy cases. Nuts and Umbelliferae (dill, carrots, celery, fennel, parsley, etc.) each represent 9.5% of cases. Allergens of animal origin are very rare in adults (Source CICBAA).