The word allergy is derived from the Greek language, from "allon ergon" in fact. It expresses the tendency to react differently, other than normal. The immune system of allergic persons reacts differently to certain substances than the immune system of non-allergic persons. The result is a hypersensitivity to various substances.

Allergic reactions have been described for centuries. Since approximately 1906 the term "allergy" has been used to differentiate between useful and useless reactions of the immune system. Many abnormal reactions of human beings after contact with certain substances which could not be explained before can now be diagnosed as allergic reactions due to todays knowlegde. The number of allergies, however, is constantly increasing lately. Scientists estimate that 30 % of the population in Germany suffer from allergies.

One of the most frequent allergic diseases is hay fever. Hay fever is mainly caused by pollen from grasses, cereals, trees, herbs or weeds. In the case of complaints throughout the year, allergens such as mites, animal epithelia or moulds might be responsible.