Final answer:
An allergic reaction is an abnormal immune response to an exposed allergen that triggers sensitization to hives, eczema, asthma, and anaphylactic shock. It involves the production of IgE antibodies and the release of histamine and other chemical mediators.
Step-by-step explanation:
An allergic reaction is an abnormal immune response to an exposed allergen that triggers sensitization like hives, eczema, asthma, and anaphylactic shock. It is classified as a type I hypersensitivity and is characterized by the production of antibodies of the IgE class. Upon initial exposure to a potential allergen, the immune system synthesizes IgE antibodies that interact with mast cells in connective tissues. Upon subsequent exposure, mast cells release histamine and other chemical mediators, leading to allergic symptoms.