Bradykinin is the primary mediator responsible for causing pain during inflammation because it directly stimulates nociceptors (pain receptors) and increases their sensitivity. It also promotes vasodilation and increases vascular permeability, amplifying inflammatory signals. Unlike prostaglandins that sensitize pain receptors, bradykinin actively triggers the sensation of pain. This makes bradykinin the key inflammatory mediator in pain induction during the inflammatory response.

Reference: Robbins Basic Pathology, 10th Edition, Volume 1, Chapter 2, Page 58