Here's a look at what's happening.
When a ring turns your finger green or black it's either because of a chemical reaction between acids in your skin and the metal of the ring or a reaction between another substance on your hand, such as a lotion, and the metal of the ring. (This may be temporary because certain foods, over the counter and prescription drugs and vitamins may cause a high acid content in your body or a drug side effect). If you are experiencing a red rash that is itchy you may be allergic to your wedding ring.
There are several metals that oxidize or react with your skin to produce a discoloration. You can get a noticeable green ring around your finger from wearing a ring made using copper. Copper is part of the alloy used to make our sterling silver. The common green or black color is not harmful of itself, though some people experience an itchy rash or other sensitivity reaction to the metal and may wish to avoid exposure to it.
A common culprit is silver, which is found in sterling silver jewelry, and as an alloying metal in most gold jewelry. Acids cause the silver to oxidize, which produces tarnish. The tarnish can leave a dark ring on your finger.
Even silver and gold jewelry can produce a discoloration, so advice for avoiding a green or black finger isn't as simple. However, certain metals are less likely to turn green or black than others. You should have good luck with stainless steel jewelry, platinum jewelry and rhodium-plated jewelry, which includes nearly all white gold.
