Freon is a word for certain chemical compounds, often used as refrigerants. Thomas Midgley, Jr. invented using Freon as a refrigerant. "Freon" is a registered trademark of DuPont. Freon was first used to describe chlorofluorocarbon (CFC) refrigerants, but it is now used to describe many other kinds of chemicals used as refrigerant. Refrigerants may contain carbon, chlorine, fluorine and sometimes bromine. For example, Freon 10 is carbon tetrachloride. Many kinds of freon are not toxic to animals. They also are cheap and work well. However, most refrigerants can reduce the amount of ozone from the upper atmosphere. Reducing ozone lets more ultraviolet light to come through. Too much ultraviolet light can cause skin cancer and cataracts, and can kill off plankton in the oceans. 