Copper begins to tarnish as soon as it's exposed to the oxygen in the air. The rate of tarnish changes when it touches the oils in our skin. The effect varies from person to person. Sometimes (not always) tarnished copper becomes shiny when one person wears it, and on others, copper will tarnish on their skin very quickly.
Copper goes through many color changes until eventually, it is a dark reddish-brown color. This is not a flaw, but a natural process. If you've ever seen an old piece of pure copper jewelry, it will be that color, with enough time and use. Some fans of copper don't like the bright color of new copper.
Copper can discolor skin a little, more or less, depending on each different body chemistry. However, the green trace can be easily washed off with water and soap.
Please look after your rings, don't get them wet as copper is a reactive metal and can leave a small green print. Pure copper will tarnish eventually, however they can always be polished and shined up again.
We suggest not wearing the copper jewelry while you are showering or doing sports activities to keep the jewelry shiny for a long time and the stain of the skin at the minimum.