E.B.
My ring does that to me all the time--I was told it was either a mild allergic reaction or just the acid on my hands (my skin oils also wore the silver off my clarinet keys in high school). I saw someone say it happened when she ovulated; I'll have to see--it was true this month! I had a jeweler tell me they could coat my ring so that it didn't do that to my skin--when it's bad, it's all the way from teh base of my finger up to the knuckle! I haven't done it; it washes off easily for me or I just take off my ring, but if it continues or bothers you, I think you can do something from the ring-end, too.