Dioxins are highly toxic and persistent environmental pollutants that are byproducts of industrial processes involving chlorine. They accumulate in the food chain and 90% of human exposure is through eating meat, dairy, fish, and shellfish. Dioxins can cause reproductive, developmental, immune and hormonal problems as well as cancer. The major sources are waste incinerators and improper disposal of industrial waste. Prevention focuses on controlling industrial processes to reduce dioxin formation and properly disposing of contaminated waste.