The answer is: contribute to ozone depletion.
CFC (chlorofluorocarbon), including freon, is used as the aerosol propellant. An aerosol is a suspension in the gaseous form of solid or liquid particles. when these compounds reach the stratosphere, UV light affects them and they release chlorine atoms. Chlorine atoms are capable of breaking down ozone molecules. With fewer ozone molecules, the ozone layer becomes thinner and harmful UV light passes through it.