Hypersensitivities are categorized according to the parts of the immune system that are attacked and the amount of time it takes for the response to occur. There are four types of Hypersensitivity reaction: Type 1, Immediate IgE-mediated, Type 2, Cytotoxic, Type 3, Immune complex-mediated, and Type 4, Delayed cell-mediated.[29] The pathophysiology of allergic responses can be divided into two phases.