This document discusses different types of hypersensitivity reactions and their mechanisms. It describes Type I reactions mediated by IgE antibodies on mast cells and basophils, Type II reactions involving antibody-mediated cell damage or lysis, and Type III reactions caused by antibody-antigen complexes depositing in tissues. Treatment involves removing allergic triggers, using mast cell stabilizers, corticosteroids, leukotriene inhibitors, and immunotherapy. Allergens that commonly cause reactions include house dust, mite feces, animal dander, pollens, and molds.