Pearls are produced by mollusks—primarily oysters—and are generally used to make necklaces and earrings. Pearls form as a defense against invasive irritants or parasites. The oyster secretes layers of a crystalline substance called nacre to coat the irritant and render it harmless.
Naturally-formed pearls are exceedingly rare. Because of their rarity, the overwhelming majority of pearls sold commercially are “cultured.” This entails prying open the shell of a live oyster and inserting irritants, and then continually stressing the oysters, thus stimulating them to secrete more nacre. Most oysters don’t survive. After some years the oyster is once again pried open and its pearls removed.
While the sentience of oysters is questionable, many vegans choose to err on the side of caution and avoid authentic pearls, natural and cultured alike. For those who have their hearts set on wearing pearls, synthetic pearls are widely available. High quality synthetic pearls can look and feel just like the real thing.