What is Allergen ?

An allergen is a substance, a particle, an organic element (atom, molecule, protein) capable of causing an allergic reaction to living being previously sensitized  by contact with the skin, inhalation, or ingestion.

An allergen is called "major" when a purified antigen triggers an allergy in 50% or more of the tested patients, and it presents specific IgE, with immediately positive skin tests, at a very low concentration, in at least 90% subjects with allergic disease in relation to this allergen. For example, peanut contains - on 7 identified allergens - 3 major allergens and a fourth which is almost.Difference

Difference between "allergic reaction" and "orthoergic reaction"

    The allergic reaction is a pathological phenomenon, related to a hypersensitivity to a substance usually without danger to health. It is the meeting between an allergenic protein and an atopic individual, genetically predisposed to allergic reaction to this protein. This same allergic reaction can also concern a potentially pathogenic substance to which the body would react in a totally disproportionate manner, which could lead, for example, to anaphylactic shock.
    The orthoergic reaction is a normal reaction to an aggressive substance.

Both symptoms may be close, but it is the responsible substance and the mechanism of onset of symptoms that is important. Tear gas, pepper, stinging nettles are examples of substances that cause manifestations similar to those caused by allergens, usually without true allergies.

Allergens

Dust, pollen, mold spores, animal hair are the most common allergens, although many other substances can become allergens for a given subject. Mites also contain several allergens from their faecal particles, salivary secretions, eggs and larvae, and dead dead mite cell debris2. They are the primary cause of respiratory allergies3 and can provoke allergic rhinitis and asthma, conjunctivitis or even a flare of atopic dermatitis.

One becomes allergic with at least two contacts with an allergen.

    The first contact causes no visible reaction: the cells responsible for the allergy become hypersensitive (by a poorly known mechanism) to a normally harmless substance.
    In the following contacts, the allergen will lead, by binding to the above-mentioned cells, a cascade of reactions leading to an allergic manifestation (from simple hay fever to anaphylactic shock, through the asthma attack). We talk about "sensitization", which can be exacerbated by cofactors or cross allergies.

Allergy is most often induced by an allergen-carrying protein that encounters an immune cell and reacts with it: in the allergic subject to this allergen, the cells responsible for the allergy (mastocyte in particular) will react to it. contact (this step does not occur in the healthy subject) and release chemical molecules responsible for allergy symptoms: histamine, serotonin, PAF, leukotrienes, prostaglandins, etc.

In particular, histamine causes vasodilatation (dilation of the veins and arteries), bronchoconstriction (narrowing of the bronchi), itching (wanting to scratch), pain: when these phenomena spread to the whole body, there is anaphylactic shock, accompanied by 'a phenomenon of anxiety (blood pressure collapses in response to dilation of all vessels, organs are not sufficiently perfused, and death occurs except in case of early treatment).

Anglosaxon studies have shown a correlation between the presence of allergens and asthma.

Food allergens, priority allergens

Currently the allergist has highlighted a list of common food allergens, and have made their labeling mandatory.
Milk, peanuts, eggs, fish, shellfish, meats, sausages, vegetables, spices, fresh and dried fruits, soy, wheat ... potentially allergenic foods are innumerable and to be tracked if you are allergic!

The development of a food allergy depends on a combination of both genetic and environmental factors. And this last century has seen a real revolution in our eating habits that would be partly responsible for an explosive increase in food allergies in the population.

Priority allergens

Severe allergic reactions (eg, anaphylaxis) occur when the immune system reacts to an allergenic protein or a particular irritant. These reactions can be triggered by food, insect bites or medication.

The associations of allergic patients have identified the substances most often associated with food allergies and allergic-type reactions. These substances are often referred to as priority food allergens. A series of consumer brochures focusing on each of the priority allergens has been developed:

    Egg
    Milk
    Mustard
    Peanut
    Shellfish
    Pisces
    Sesame seeds
    Soy
    sulfites
    Nuts
    Wheat and triticale