Allergies:

Airborne Allergen: an allergen carried through the air and inhaled (synonym of " 
pneumallergen ").

Allergen: a substance which causes an allergic reaction in some subjects.

Allergic Breakthrough: activation of IgE suppression mechanisms during a viral infection 
allowing IgE production in the presence of the allergen. This results in an allergic reaction.

Allergic Reaction: changes induced in the body following contact with an allergen to which 
the body had been previously sensitized.

Allergy: excessive and specific reaction of a person in contact with a foreign substance or 
allergen that does not induce a disorder in the majority of subjects. The allergy occurs when
 this person has been previously affected by the same foreign substance (sensitization).

Anaphylactic Shock: an acute allergic reaction which consists of the most serious allergic 
reaction and vascular failure (a drop in blood pressure). All allergy symptoms can be 
observed during such a reaction.

Anaphylatoxin:  a property of the substance C3a and C5a released by the C3 and C5 
complexes during activation of the complement.

Anatoxin: a non-toxic derivative used for vaccination.

Anergic: characterized by an inactive T lymphocyte.

Angioedema: an allergic reaction characterized by sudden facial swelling with edema of the 
lips, eyelids and certain mucosa or other parts of the body. It can prove to be dangerous 
when it affects the pharyngeal or laryngeal mucosa. Swelling then impedes breathing and 
can cause true asphyxia.

Anosmia:  total loss of smell.  It can be accompanied by loss of taste (ageusia).

Antibody: a specific defensive protein in the blood, secreted by "B lymphocytes" in 
response to the introduction of a foreign substance or antigen in the body. The antibody 
combines with the foreign substance to neutralize its toxic effect.  Synonymous with 
"immunoglobulin".

Antigen: a substance which is foreign to the organism and can trigger an immune reaction 
by inducing the formation of antibodies. 

Antihistamine: a medicinal product which fights the action of "histamine". It does not prevent 
histamine from binding to its receptor but blocks activation of the cell involved.

Asthma: a disease characterized by acute episodes of paroxysmal wheezing dyspnea,  a 
sign of sudden contraction of the muscles which control the opening and closing of the 
bronchi; such episodes can be accompanied by edema and mucosal hyper-secretion of the 
airways (pharynx, larynx, trachea and nasal fossae).

Atopy: the hereditary predisposition to develop allergies such as asthma, hay fever (or 
pollinosis), urticaria, eczema (so called "atopic" dermatitis), certain other types of rhinitis and
 conjunctivitis as well as different food allergy reactions.

Auto-Immunity: a pathologic condition where the body produces antibodies against its own 
tissues. 

Avoidance (of an allergen): removing an allergen from the environment with the aim of 
avoiding an allergic reaction.