The term "ozone depletion" actually refers to two separate events: the steady decline of ozone in the stratosphere at a rate of 3% per year, and the seasonal decrease of the ozone layer over the polar region. This layer protects the Earth from the effects of ultraviolet light (UVB); a steady decrease of ozone means that more of these rays actually reach the surface of the planet, increasing the risk of skin cancer, and affecting everything from plankton populations to crop production.
The main culprits in the destruction of the ozone layer are chlorofluorocarbon (CFC) compounds, also known as freons, and bromofluorocarbon compounds, also known as halons. CFCs are used mainly as refrigerants. Until 1995, they were the base compound used in aerosol sprays, air conditioning units, and as cleaning agents for electronic equipment. Since then, the Montreal Protocol has prohibited their use in commercial products, and urged manufacturers to replace CFCs with chemicals that cause less damage, such as hydrochlorofluorocarbons (HCFCs), which affect ozone 90% less than CFCs.
Some of the most common products containing chemicals that destroy the ozone layer include aerosol inhalers for asthma sufferers and fire extinguishers. While active production of CFCs is already banned in the US, many countries around the world are still manufacturing them or selling products that contain them, like solvents, aerosol sprays, foaming agents used in factory settings. CFCs from car air conditioners were once a major problem, but a new system in cars now recycles CFCs rather than releasing them into the atmosphere. This is only true in newer models, however, and cars in developing countries and models made before 1993 still have the old system. The same is true of the CFCs present in refrigerators and air conditioning units in houses and buildings.
HCFCs, while less damaging, still cause problems. They are being phased out of production, but official sources estimate a total ban won't happen until 2030. If all use of CFCs and HCFCs stops, the ozone layer may eventually repair itself.