The term chemical agent refers to any substance that can cause a change in an organism, tissue or environment. This includes both naturally occurring and synthetic compounds, which may be used for various purposes such as cleaning, agriculture, medicine, and warfare. In the context of warfare, chemical agents are typically poisonous gases or liquids that can cause harm to living organisms through inhalation, ingestion, skin contact, or other means. Examples include mustard gas, sarin, and VX nerve agent.