Which type of allergic reaction is characterized by hives?

The type of allergic reaction characterized by hives, or urticaria, is Type I hypersensitivity. This form of hypersensitivity occurs rapidly upon exposure to an allergen, typically within minutes. It is mediated by immunoglobulin E (IgE) antibodies, which trigger the release of histamine and other inflammatory mediators from mast cells and basophils when they bind to the allergen.

The resulting histamine release leads to the classic symptoms of hives: raised, itchy welts on the skin as well as other systemic symptoms such as swelling (angioedema) and respiratory distress in severe cases. This immediate and often dramatic response is typical of an IgE-mediated reaction, where exposure to the allergen can cause a cascade of physiological changes within a very short time frame.

In contrast, the other types of hypersensitivity reactions involve different mechanisms and timeframes. Type II hypersensitivity is mediated by IgG or IgM antibodies against cell surface or matrix antigens, leading to cell destruction or dysfunction. Type III hypersensitivity involves immune complexes forming in circulation, which can deposit in tissues and lead to inflammatory responses. Type IV hypersensitivity is a delayed-type reaction mediated by T cells, usually occurring hours to days after exposure to an