Rings, piercings and metals

I was buying an engagement ring the other day. The clerk was telling me about the composition of different rings. One set of rings was made of palladium, a metal which I've read is potentially dangerous.

That got me thinking about the composition of the rings, piercings and other jewelry people wear and wondering if they might have dangerous metals in them which could leech into a person's body if worn next to the skin for long enough.

This may just be paranoia on my part, but I wonder if anyone has found any information or has any opinion about this.