For the development of an allergy interactions between T- and B-lymphozytes with an antigen- the so-called allergen- are of importance. Following this interaction large numbers of IgEs are produced. These IgEs are antigen specific and bind to mast cells that will release histamine. This initial reaction of a first encounter with an allergen does not result in allergic reactions. A second contact with an allergen is necessary in order to facilitate an allergic reaction. The coupling of an IgE and a mast cell then releases histamine, leukotrienes and prostaglandins. These are mediators of inflammatory symptoms and cause the typical allergic symptoms, such as itching, swelling and rhinitis, the infamous hay-fever.

The precise reasons for the increase in individuals affected by allergies are not known. Possibly a combination of life-style changes in industrialized nations is partly to blame. An increased exposure to toxic substances may be another culprit. Related to this our nutrition has received much attention by scientists.

Less frequent than the described type I allergies are type II allergies based on autoimmune reactions caused by antibodies such as IgE and IgM. Also infrequent is the type III that that leads to so-called immune-complexes, i.e. the aggregation of a large number of antibodies, leading to severe inflammations, and the type IV that is signified by an activation of T-cells. Since allergies belong to the inflammation reactions in rare cases anaphylactic shocks may occur. Anaphylactic shocks are caused by extreme dilation of blood vessels, reduced blood pressure and a restriction of the bronchia, leading to respiratory arrest, and eventually death.