CFCs were once a common chemical compound used in refrigerants and aerosols until it was discovered how damaging they were to the ozone layer. The Montreal Protocol is an international treaty that was passed with the goal to eliminate the usage of CFCs and other ozone depleting chemicals.
Due to the usage of these chemicals, there are holes in the ozone layer across the world, notably in the Antarctic region, which allows dangerous amounts of UV radiation from the sun into the atmosphere. Overexposure to UV radiation can lead to serious health issues, including cancer.
More information: NASA