Why does the gold coloring on costume jewelry rub off, and is there a way to prevent it?

So I have a bunch of gold colored costume jewelry that on all of them, as soon as I wear it and start sweating a bit (especially my necklaces) the finish rubs offf and now it’s the silver color of the metal underneath. Is there a way to prevent this from happening? It doesn’t happen with my silver colored costume jewelry, unless I just don’t notice it because the silver finish is wearing away to a silver metal. I want to be able to wear/buy more gold toned costume jewelry but I don’t want to if this is going to happen with all of it!