The process of pearl formation inside an oyster is essentially a natural defense mechanism.

 The process of pearl formation inside an oyster is essentially a natural defense mechanism.

Entry of a foreign object: When a grain of sand, a parasite, or a tiny particle accidentally enters the soft tissue (mantle) of the oyster, the oyster experiences discomfort.

Self-defense: To alleviate this discomfort or irritation, the oyster begins to secrete a type of iridescent fluid from its body. In scientific terms, this is called nacre or 'mother of pearl'.
Layer formation: The oyster continuously deposits layers of nacre around the grain of sand or parasite. This is similar to a gift-wrapping process.
Pearl formation: Over the years, thousands of layers of nacre accumulate, gradually transforming into a lustrous and hard pearl.