Which condition is an example of a type I hypersensitivity reaction?

A type I hypersensitivity reaction, also known as an immediate hypersensitivity reaction, is characterized by an allergic reaction that occurs quickly after exposure to an allergen. Anaphylaxis is a severe and potentially life-threatening allergic reaction that involves multiple body systems and is mediated by the release of immunoglobulin E (IgE) antibodies. When a susceptible individual is exposed to an allergen, it triggers the immune system to release histamines and other substances leading to symptoms such as difficulty breathing, swelling, and a rapid drop in blood pressure.

This rapid response distinguishes it clearly from other types of hypersensitivity reactions, like serum sickness (a type III hypersensitivity reaction), contact dermatitis (a type IV hypersensitivity), and blood transfusion reactions (which can involve type II hypersensitivity). Anaphylaxis exemplifies the classic features of type I hypersensitivity, including the immediate onset of symptoms and the role of IgE and mast cells in mediating the response.