A causal agent is an entity or factor that is responsible for causing a particular event, phenomenon, or condition. Synonyms for the word include "cause," "originator," "source," "force," "trigger," "stimulus," "influence," "underlying factor," "root cause," and "precipitating factor." These terms are often used interchangeably to explain or describe the cause of an occurrence, whether that may be a scientific phenomenon, a medical condition, or a social issue. A clear understanding of causal agents can help researchers, physicians, and policymakers identify the most effective solutions to address them and prevent their negative effects.