In the dry language of doctors, an allergy is a pathological reaction of the immune system associated with hypersensitivity to certain substances – allergens. However, it is not enough to eat a new fruit or rub your cheek against a cat in order for you to develop an allergy. You need sensitization – increasing the body’s sensitivity to a substance, which subsequently will be an allergen.

Allergens are divided into two types. If they enter the body from outside, they are called exoallergens (from the Greek ἔζω (exo) – from outside, from the outside).

If allergens originate inside the body, they are called endoallergens (Greek ἔνδον (endo) – from inside, inside) or autoallergens (from Greek αὐτόζ – itself). For example, such allergies often develop to proteins secreted by the body during a rheumatic process. It helps against some of them:

Mechanism for the development of an allergic reaction
Every day we are faced with thousands of substances foreign to the body:viruses, bacteria, pollen, insects and animal products, products, medicines, industrial emissions and many others.

When such a substance enters the body, the process of producing antibodies – special protein compounds that are designed to neutralize the effects of foreign substances. That is, antibodies are a kind of guards inside us. At the same time, each antibody is responsible for neutralizing one foreign substance.

If the immune system fails, antibodies are produced in excessive amounts. When the allergen enters the body again, they are activated and trigger a cascade of biochemical reactions resulting in the production of special substances, including histamine. Its sudden release, in particular, leads to the development of allergy symptoms and their various manifestations.

In order to become clearer what allergies are, and what their causes are, let’s find out what types of allergic reactions exist. There are four in total. However, some allergic reactions can be combined, combining 2-3 types of allergies.1, 2

Type I – Reactive or IgE-conditioned allergic reactions. In response to exposure to the allergen and the development of sensitization to it, special IgE antibodies are produced. Active release of substances (histamine, leukotrienes, etc.) causes acute allergic reactions in blood vessels, skin and other organs and systems of the body. For example, allergic rhinitis (runny nose), allergic conjunctivitis (symptoms are clearly manifested on the mucous membrane of the eye – conjunctiva), bronchial asthma, etc.1

Type II – cytotoxic. Cells are damaged due to the formation of antibodies, the damage may be due to:

complement activation and damaging action of its fragments;
damage and dissolution of cells with antibodies by special NK-cells – so-called antibody-dependent cellular cytotoxicity.

Allergic reactions in this case can lead to complications after transfusions of blood and its components, blood diseases associated with the immune response. 1, 2

Type III – so-called immunocomplex allergic reactions. Antibodies either react incorrectly to body tissues or the tissues themselves are altered so that they become foreign. As a result, the immune system rapidly and ruthlessly attacks them, and diseases such as serum sickness, systemic lupus erythematosus, rheumatoid arthritis and other systemic autoimmune diseases develop.

Type IV are delayed-type allergic reactions. They are associated with immune activity and develop due to changes in lymphocytes. Most often they are possible with contact dermatitis, rejection of transplanted tissues, manifestations of tuberculosis, brucellosis, leishmaniasis, etc.