To clean yellowed cultured pearls, use a soft damp cloth and use pearl cleaner. Other jewelry cleaners and liquid soap can damage pearls further.
Yellowing of pearls can be caused by age, improper care, or exposure to damaging materials, such as perfumes and hairsprays. The best way to ensure that pearls are in their best condition is by washing them with a soft, damp cloth after each time they are worn. If they become too yellowed, its advised that they are taken to a jeweler that specializes in repairing pearls.
Never use ammonia or chlorine to clean pearls, as these can quickly damage pearls and make it nearly impossible to fix them. Instead, try using a touch of olive oil can help restore the pearls natural luster.