In order to retain the quality do NOT use cleaning methods which involve soaps containing ammonia, or any type of harsh soaps and detergents. Those will harm the surface, and eventually deteriorate the pearls.  Do not expose your pearls to bleach or powdered cleansers such as baking soda or other scrubbing agents.

Beware of using jewelry-cleaning solutions that are made general use on jewelry and gemstones. The nature-made pearls (authentic) are slightly porous and will be damaged by those solutions. But do not use the same for pearls, as these are porous and can absorb the agent.

Any use of steam or hot water is to be avoided. The combination can be very damaging to the pearl.

General rules of thumb: DO NOT soak or wash pearls with hot soapy water, detergents, cleansing agents or solutions.   

No matter how "gentle" they are said to be, it is DO NOT use ultrasonic gem cleaners for cleaning your pearls. And avoid any use of hot water or steam cleaning methods. 

Instead of any harsh or caustic cleaning that is damaging to the pearl, it is recommended to use a soft cloth to clean, and at most, a warm, very mild soapy swish and rinse. Then, it is recommended that you have a professional jeweler clean and check your pearl jewelry, about every six months to assure that mountings and threads are in good repair. Follow the pearl care guide that comes with your pearl jewelry purchase.