There are four types of hypersensitivity reactions, classified as Type I to Type IV:
Type I: Also known as immediate hypersensitivity, it includes allergic reactions such as hay fever, asthma, and anaphylaxis. Type II: Also called cytotoxic hypersensitivity, it involves the destruction of cells mediated by antibodies, such as in certain drug-induced hemolytic anemias. Type III: Known as immune complex-mediated hypersensitivity, it involves the formation of antigen-antibody complexes that precipitate in tissues, leading to conditions like serum sickness. Type IV: Also known as delayed-type hypersensitivity, it involves T-cell mediated responses, such as contact dermatitis from exposure to nickel or poison ivy.
