High acid sweat can cause a reaction between the metal and the skin which in turn causes the color of your skin to turn black, not due to the gold itself.
Lotion or oils get trapped between the skin and when combined with the heat of the sweat, it may cause your finger to turn black
In my career, I’ve heard and seen it repeatedly. Occasionally, clients complain about their skin turning black and they think gold is the cause of it.
Gold itself does not contain any material that causes discoloration and it does not release any kind of chemicals even if 14 Karat has 580% pure gold content, 24-karat does not cause discoloration.
So, if you experience anything like that you should check your acid content or your iron content as to why your sweat is causing it.
In my 35 years of experience, I’ve seen a very small amount of cases like these, but they do happen.
Recently this happened to one of my clients. I took my client to check the gold assay and the gold did not reveal anything unusual. We then wore the gold for 24 hours just to see if anything the gold was doing proved that the client had an issue and not the gold; in the end, it did not cause any discoloration.
If you hear about this or it happens to you, this is pretty much what happens.
You get discolorations from the gold by wearing it. This could also happen with any type of metal between your skin, the sweat could accumulate and cause discoloration. It’s not harmful though, all you must do is remove the gold, wash your hand with soap and it will go away. This won’t happen all the time since it is the sweat that causes it to happen.