The contact of the allergen with the immune system allows allergy antibodies (IgE) specific to that allergen to be produced in a person genetically predisposed to (atopic) allergies. The person is then sensitised to that allergen. After the allergen is recognised by the molecule of IgE, allergic inflammation can be induced, with clinical symptoms as a consequence. This is then called allergy.
It is important to remember that a patient can be sensitised to a particular allergen without developing allergic symptoms, even when exposed to that allergen. Thus, the diagnosis of allergy requires evidence of both sensitisation and allergic manifestations related to that allergen.
In this chapter, you will get an overview of the different allergic diseases. Some of them, such as eczema or asthma, do not always have an allergic origin. The doctor will not limit himself to proving allergenic sensitisation with his examinations, but will also look for other causes.