What type of hypersensitivity reaction is associated with allergies?

Type I hypersensitivity, also known as immediate hypersensitivity or anaphylactic hypersensitivity, is the type associated with allergies. This response is mediated by immunoglobulin E (IgE) antibodies. When an individual who is sensitized to a specific allergen is exposed to that allergen again, the IgE antibodies trigger the degranulation of mast cells and basophils, leading to the release of histamine and other inflammatory mediators. This results in various allergic symptoms, such as itching, hives, nasal congestion, and in severe cases, anaphylaxis, which can be life-threatening.

The other types of hypersensitivity reactions involve different immune mechanisms. Type II hypersensitivity is mediated by IgG or IgM antibodies directed against antigens on cell surfaces or in the extracellular matrix, leading to cell lysis or dysfunction. Type III hypersensitivity involves immune complex formation that deposits in tissues, resulting in inflammation and tissue damage. Type IV hypersensitivity is delayed-type and is mediated by T cells rather than antibodies, leading to inflammation and tissue injury over hours to days after exposure to the antigen. Each type has distinct mechanisms, but Type I is specifically responsible for the rapid allergic reactions commonly seen in various allergic conditions.