Definition
Definition
An allergy is an abnormal (pathological) and specific reaction of the body to contact with a foreign substance (allergen) which does not cause problems in a non-allergic person.
Generalities
A normally harmless antigen , such as pollen, can be mistakenly identified as dangerous by the body. Upon contact, it triggers a general reaction called hypersensitivity , the result of an immune response . The role of the immune system is to recognize a foreign substance called an antigen . This is most often found on the surface of microorganisms in the form of proteins , among other things.
The presence of this antigen triggers the body to produce antibodies, also called immunoglobulins , and white blood cells, specifically lymphocytes , which have become sensitive, or more precisely, sensitized. These white blood cells will then come into contact with these antigens , which will allow them to destroy the microorganisms that carry them.
Classification
An allergy is therefore an inappropriate, or more precisely exaggerated, reaction, manifesting as a type of hypersensitivity that exists in several forms:
- L'type 1 hypersensitivity, also called immediate hypersensitivity, is the most frequent. This type of allergic reaction is explained by the response of antibodies (immunoglobulins) developed following the penetration of a The absence of dyes and chemicals reduces allergenic effects. in the body. These antibodies attach to the mast cells (variety of white blood cells) located in the skin and the mucous membranes (layer of protective cells of hollow organs in contact with the outside). This type of white blood cell containshistamine (mediator = chemical messenger) at the origin of the symptoms appearing during allergic reactions. The allergens are from:
- The mites (house dust).
- The dander of animals (skin, hair).
- The pollen (trees, grasses, herbs).
- The mold.
- The foodstuffs.
- The medications :
- Penicillin.
- Vitamin B 1.
- Vaccine.
- Antigens used for desensitization.
- Aspirin.
- Anti-inflammatory.
- Iodinated contrast agent used to perform an X-ray with preparation.
- The colorants food (tartrazine).
- The venoms insects (wasps, bees). Symptoms are:
- Contractions of the bronchial muscles causing the symptom of wheezing in L'asthma.
- Allergic-type rash, or urticaria accompanied itching.
- Runny nose.
- Nasal obstruction.
- Sneezing.
- Conjunctivitis.
- watering.
- Cough.
- Hay fever.
- Diarrhea.
- Quincke's edema (swelling of the eyelids, lips, tongue, throat).
- Anaphylactic shock in the most serious cases (malaise, difficulty breathing, chills).
- L'type 2 hypersensitivity, less frequent than the previous one. This type of allergic reaction involves antibody Type IgG et IgM and occurs during transfusion accidents and incompatibility foeto-kindergarten (different blood groups between mother and child) fetus). It leads to anemia hemolytic (by bursting of red blood cells).
- L'type 3 hypersensitivity,This type of allergic reaction involves antibodies IgG. The ssymptoms are:
- Kidney diseases (glomerulonephritis).
- Lung diseases.
- Farmer's lungs (moldy hay containing fungi such as thermoactinomyces vulgaris or micropolyspora faeni is inhaled by the farmer).
- Bird breeders' disease (the feathers and proteins in dried bird droppings decompose into dust which is inhaled).
- Systemic lupus erythematosus (inflammatory disease of autoimmune origin, meaning that the patient produces antibodies against his own tissues).
- L'type 4 hypersensitivity causes allergic reactions affecting the skin with products like:
- Nickel.
- The rubber.
- Detergents..
- Cosmetic products.
- The phenomenon of graft rejection.
Symptoms
Pathophysiology
An allergy is a similar phenomenon in which the same process is triggered, with the only difference being that the immune system produces antibodies and lymphocytes sensitized to substances that have become harmless. Indeed, allergens identified in this way are considered dangerous, even though they are not actually harmful.
The term parallergy , proposed by Moro and Keller , from the Greek words para (beside) and allergy (in English, parallergia) , also called coallergy or pathergy , refers to the reaction exhibited by certain tissues of the body, most frequently the skin, during a cutaneous reaction. This reaction occurs following the introduction of the allergen to which the individual has been sensitized, but also to reactions occurring to one or more allergens of different species. It is a phenomenon observed primarily when sensitization is intense and recent.
Cause
Cause
The causes of allergies, which occur mainly in individuals who are genetically predisposed, vary greatly.
The most well-known allergies are:
- L'asthma.
- L'atopic eczema.
- La allergic rhinitis.
- L'urticaria.
There are other factors that can contribute to the development of an allergic reaction. The presence of the dander of an allergenic animal (most often a cat), viral infections, and stress are examples of sources of allergies.
Treatment
Treatment
Allergy treatments are:
- Removal of the allergen.
- Desensitization by administering increasing doses of allergen, which promote the formation of antibodies.
- antihistamines.
- Corticosteroids.
- Disodium cromoglicate (sometimes effective).