Dioxins are produced as pollutants in industrial production processes and during incineration (e.g. of waste). Thanks to their highly lipophilic nature and long half-life in fat tissue, they accumulate in the food chain. One of the most important initial steps in the toxicity of dioxins is the activation of a cytosol receptor. This induces the production of a number of proteins, including cytochrome P450 CYP1A1. Our knowledge about the effects of dioxins in humans is based primarily on long-term epidemiological studies of people who were exposed to high concentrations of dioxins, either occupationally or as the result of an accident. The best known and most definitely established effect of exposure to dioxins is chloracne. Whether there is a relation between exposure to dioxins and other diseases, such as cancer, is uncertain.