An allergy is an exaggerated reaction of the immune system to an allergen. In the healthy individual allergens are recognized by the immune system, but do not cause any symptoms. In allergic patients this allergen tolerance is broken and the immune system starts to produce Immunoglobulin E (IgE). The allergy diagnosis is based on allergen specific IgE that can be tested in blood or by skin challenges (prick tests). Allergens are usually proteins, the most common are present in pollens (birch, grass), house dust mite, moulds, pets’ fur and different food components.

Typical allergic disorders include allergic rhinitis - hay fever -, asthma, atopic dermatitis - eczema - and other skin complaints, conjunctivitis - irritation of the eye -, food and drug hypersensitivities, and anaphylactic shock - for example, in reaction to a peanut allergy.
The disease often progresses from atopic dermatitis to allergic rhinitis and then to asthma. This evolution, known as “allergy march”, needs to be carefully followed and treated.