How do you take care of your cultural Pearls?

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My pearl necklace as a cute little pearl in it. It is so worn down that I can actually see the layers in which the pearl was formed. My ring has a nice nice pearl in it with two small diamonds on the side. This pearl actually came from one of those diving for pearls at the San Diego Sea World. It too has the shine taken right off and and is so worn down on the one side it actually cannot be called round anymore. More like a egg shape and very dull. Why do my pearls react like this?