Dioxin is a generic term for a group of more than 200 complex compounds, all of which contain chlorine (specialist name: polychlorinated dibenzodioxins and furans, PCDDs and PCDFs). Seventeen of the compounds in this group have been found to be toxic to varying extents. Their impact on living organisms varies greatly from one animal species to another.

Dioxins in trace quantities are created naturally (e.g. by volcanoes) and as unintentional by-products in numerous combustion processes (e.g. forest fires, cigarettes, bonfires, car engines etc.), in metal smelting and recycling processes. Only a small proportion comes from the chemical industry.