This prevents tarnishing inside the stone, where it cannot be cleaned and may discolor over time. The first time you put them on the earring wire, do so with the earring off your ear. Twist the rubber stopper onto the wire. Once the stopper has been broken in, they are easy to use. Many people tell me they are allergic to anything except 14 karat gold.
Most people are allergic to the nickel in metal.
All of the earrings I make with posts are made using nickel free posts unless otherwise noted. If you are allergic to metal, try a pair of these, but make sure you use the nickel free back. I have been unable to find a quality vendor for nickel free wire or French ear wire findings.