An allergy is an excessive reaction of the organism to foreign bodies or substances normally tolerated by the body. These can be flower and grass pollen, animal hair, excrement of house dust mites, ingredients of food, spices, chemicals or fragrances and cosmetics. Where the basic willingness to develop an allergy comes from has not been fully researched.
- Hereditary influences (variants have now been identified in more than 50 different genes (including ADAM33, GPRA or IL1RN, which all play a role in allergic inflammation)
- Underestimulation of the immune system in early childhood with viral or bacterial pathogens, e.g. through excessive hygiene (surface disinfection)
- The immunoglobulins of type E (IgE), which mainly occur in many allergic reactions, were originally used to defend against infections with parasites such as tapeworms, which have become rarer in industrialized countries.
- Unfavorable nutrition, in discussion are certain fatty acids, the high histamine content in certain foods, and vitamin D, which has an immunosuppressive effect
- Due to fine dust and house dust, which increases the aggressiveness of pollen and the body's ability to absorb allergens
- Psychosomatics, but more than a secondary phenomenon in the sense of conditioning for allergenic stimuli
- Increase in pollen flight, e.g. due to global warming or as a stress reaction of trees to pollution
- Increase in mite exposure due to better insulation of houses
- Early changes in the intestinal flora, which can be influenced by antibiotics and probiotics
- Change of the skin flora e.g. through the introduction of diapers
- Cold-resistant bacteria in food e.g. through the introduction of refrigerators
- Drugs, e.g. paracetamol
- Cigarette smoke - smoking parents can increase the probability of allergy eightfold
Since the vaccination coverage in the New Länder was significantly higher until 1989 (close to 100%), but allergies were almost unknown despite higher environmental pollution (e.g. from lignite combustion), this explanation is not considered very valid. In the meantime, several epidemiological studies also refute a connection.
When an allergen has crossed the first barrier (skin or mucous membranes) and is recognised by the immune system as a foreign body, B-lymphocytes are stimulated to produce the antibody (type E immunoglobulin) that is suitable for the allergen. This takes one to two days. This process is called the sensitization phase, because the organism is immediately able to produce the corresponding antibodies upon further contact with these allergens. The production of antibodies at the first contact with an allergen does not yet trigger any symptoms. The antibodies formed attach themselves to the surface of mast cells and are thus able to bind the allergens to the mast cell on renewed contact. As a result of the binding, the membrane of the mast cells becomes permeable and the vesicles stored in them release the histamine, which initiates an inflammation cascade that leads to the known symptoms.
The reasons for the increase in allergies in the population have not yet been fully clarified. One theory is the "hygiene or jungle hypothesis". It states that there are many allergy patients in countries with a high standard of hygiene because they had too little contact with pathogens in early childhood, when the immune system was formed. According to this theory, an allergy would be a kind of substitute action of the immune system in which, in the absence of real pathogens, even harmless substances become the target of an immune response. However, this is a mechanistic understanding of the complex immune regulation. Another theory is the "survival hypothesis". According to this hypothesis, many children who would have become victims of the high infant mortality rate due to respiratory infections at the beginning of the last century survive today due to improved living conditions. As a result, certain gene variants may have increased in the population, which are now responsible for some of the "civilisation" diseases.