This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
Both metal and copper oxidize when exposed to oxygen and this is a natural process. Copper that is exposed to the outside environment is more likely to turn green and that is why copper vases and decorative pieces in gardens are often green.
But after you wear one for a while, you might notice that the skin underneath the copper turns green. This is a normal reaction that occurs with any kind of prolonged copper exposure on the skin. The green color will fade if you stop wearing the copper, and it is not harmful to your health.