The ozone layer is a high level layer of gas in the stratosphere. The ozone helps to keep out harmful UV rays, which cause sunburn and damage plants.
CFCs were used in aerosols, such as hairspray cans, fridges and in making foam plastics.
The resulting ozone holes let harmful UV radiation in and add to the problems of the greenhouse effect and global warming, as the diagram below explains.
CFCs were banned in many countries in the mid-1990s after it was found that they were breaking up the Earth's ozone.
Some scientists now say the hole in the ozone layer over Antarctica could disappear within 50 years as ozone levels are stabilising.
The pie chart below shows the gases responsible for the enhanced greenhouse effect.