Allergic diseases can have very different manifestations, as hay fever, asthma, food allergy, or atopic dermatitis. These diseases share the following mechanism: Involving antibodies, a foreign stimulus leads to the rapid activation of cells that initiate an inflammatory response. Allergic diseases are an example of immune responses that have gone awry. The Western lifestyle has led to a massive increase in such diseases since the 1960s. Originally, allergic reactions were directed against parasites, but these pests hardly play a role for us anymore. Thus, in our modern society, they no longer serve any biological purpose.