Which substance is primarily responsible for causing inflammation in an allergic or hypersensitivity response?

Histamine is a key mediator in allergic and hypersensitivity responses. When an allergen is encountered, the immune system reacts by triggering the release of histamine from mast cells and basophils. This substance plays a crucial role in the inflammatory process by causing vasodilation, increasing vascular permeability, and stimulating sensory nerves, leading to the classic symptoms of allergies such as redness, swelling, itching, and increased mucus production.

While cytokines and interleukins are important in immune responses and can contribute to inflammation, they primarily function as signaling molecules that influence the behavior of other immune cells rather than being direct mediators of the acute inflammatory response characteristic of allergies. Serotonin, although involved in various physiological functions, does not play a primary role in triggering the inflammatory processes associated with allergic reactions. Therefore, histamine is the main substance you associate with the inflammation seen in allergic and hypersensitivity responses.