Because salt water pearls have only a thin layer of nacre, caring for them should be at the top of your jewelry-care to-do list. This doesn't mean, however, that you should ignore those gorgeous freshwater pearls.
Pearls are an organic gemstone. Organic gemstones are those stones like pearls and coral that are acquired from animals, and not stones that formed after years of certain heat and pressure criteria. Organic gemstones are softer and more fragile than other stones and therefore need a bit more attention and care.
The use of cosmetics, hair sprays, perfumes, and the like can dull the luster of your pearls over time. Even your own body oils and perspiration can affect the brilliance of them. That said, it is always good practice to apply any perfumes, hair sprays, or other cosmetics before you put on your pearls. This will help ensure that the pearls come into contact with the products as little as possible. After wearing your pearls, it is good practice to wipe them off with a soft damp cloth to clean off any cosmetics residue. To remove any buildup that's accumulated over time, wash your pearls with a mild soap and water.
Since pearls are relatively soft and fragile, it is best to store them away from your other jewelry. For this reason all my pearl jewelry is packaged in a soft cloth bag that makes it easy to keep it apart from your other stones and metal but allows you to keep it in the same jewelry box. I also send a soft cloth so you can clean your pearls.
In the case of a knotted pearl necklace - which is generally strung on silk cord - it is a good idea to get it restrung every so often. This is so that you avoid the string eventually breaking. If you notice the cord fraying at any point, stop wearing the pearls and get them restrung. The technique of knotting the strand after each pearl comes from when pearls were found more by chance, and later when they were cultivated but still muy expensive, to keep the loss of the gems down should the cord break. Keep in mind a necklace is most likely to break at the clasp or at a point that is constantly messed with. So, if you're a person who like to twirl their necklaces, don't do it. That's most likely the spot the necklace will break.