from an IgM antibody class switches into IgE). The generation of an IgE antibody against an antigen is known as sensitization. This is much more likely to occur in atopic individuals. Sensitization on its own does not guarantee that a type I hypersensitivity reaction will occur.

Once the IgE has been generated, it binds primarily to mast cells via the high-affinity IgE receptor (Fc?RI) expressed on mast cells and basophils.