It is estimated that 25 to 30% of the population is allergic to something and this proportion is constantly increasing. Air pollution, more (too?) rigorous hygiene, increased use of drugs, new diets or even changes in our indoor environment could explain this increase. What exactly are the mechanisms associated with an allergy?
Very briefly, an allergy can be seen as an exaggerated immune reaction to a substance that should in theory be tolerated by the body, called an allergen. We now know that the majority of allergies are caused by antibodies, class E immunoglobulins (IgE). Allergies particularly affect children and young adults, but they can actually occur at any age, especially in people with a genetic predisposition. Some studies also suggest that children born by caesarean section have an increased risk of allergic disease (because they have not been exposed to the maternal microbiome).
Allergies can be triggered by food, medication, animal hair, pollen, Hymenoptera venom, metal contact, etc. An allergy can manifest itself in various ways:contact with the allergen can trigger a skin reaction (dermatitis, urticaria), respiratory reaction (allergic rhinitis, asthma) or in the most serious cases, anaphylaxis, the outcome of which can be fatal.
Our immune system is able to recognize a harmful foreign body (bacteria, viruses and parasites) as soon as it enters the body; it then produces cells capable of eliminating this intruder. But in the case of an allergy, the immune system is disrupted:it no longer tolerates certain substances that are harmless. These substances, called allergens — which are almost always proteins — stimulate the immune system, which begins to produce a specific series of antibodies; these in turn trigger the massive release of chemical mediators (histamine, tryptase, leukotrienes, prostaglandins, etc.).
For example, when mast cells come into contact with an allergen and they present IgE specific to it on their surface, they release histamine, which will cause more or less serious reactions (vasodilatation, pruritus, edema , watery eyes, runny nose, etc.), well known (and feared) by people with allergies.
In non-allergic people, the normal function of IgE is to fight against parasites. These antibodies thus circulate in a free state in the blood serum and are also found associated with cells of the immune system of the skin, lungs and digestive tract (which explains the localization of allergic symptoms).
The first time someone is exposed to an allergen, they usually don't experience a reaction because it often takes time for the immune system to develop a sensitivity to the substance. But as it learns to recognize the allergen, it begins to make antibodies to attack it as soon as further exposure occurs.
Note that the type of allergen, as well as the mode of entry into the body will determine the external physical manifestation of allergies. Thus, exposure to skin allergens generally results in redness, itching, swelling and a burning sensation of the skin, while pneumallergens - which enter the body through the air and respiratory route - can cause runny nose, chest tightness and breathing difficulties.
Among the most common allergens are:
Some allergies are seasonal. For example, allergic rhinitis (also called hay fever)—the most common manifestation of respiratory allergy—usually peaks between April and May, when the number of pollens in the air is highest. This allergy can also be due to dust mites and cats; in these cases, the risk persists throughout the year.
There is no cure for allergies; drug treatments (antihistamines, corticosteroids) or desensitization strategies — which aim to make the patient tolerant to the responsible allergen, via the regular administration of small amounts of allergen over several months or years — allow however, to improve the living conditions of people with allergies. However, avoiding the responsible allergens remains the best way to limit allergic reactions.
To reduce exposure to household allergens, here are some simple tips:
The number of people with allergies has increased markedly over the past two decades, especially among children. The Global Allergy &Airways Patient Platform warns that allergic problems will increase further as air pollution and ambient temperature increase. Indeed, these environmental changes, inherent to human activity, will affect pollen counts, the presence or absence of biting insects and the presence or absence of molds associated with allergic diseases.
