What damages the ozone layer the most?

Chlorofluorocarbon gases (CFCs) eat the ozone layer alive where we use it everyday for industrial processes although the ozone layer can repair Itself.

Another answer:

The number one reason ozone thins in our atmosphere is due to a lack of sunlight. Without this energy, ozone naturally will decay into oxygen molecules. This is why the hole in the ozone layer only appears over the poles and then only at the end of the winter months at each pole. Once the sun returns, these holes quickly disappear.