Hardness and toughness
The Mohs scale is the most commonly used scale used to measure gem and mineral hardness. Pearls are ranked 2.5 on the Mohs hardness scale, which means that they’re very soft and can easily be scratched or abraded. But with reasonable care, any pearl jewellery can be a lasting treasure.

A pearl’s toughness is usually robust, but age, dehydration, and sometimes excessive bleaching during initial processing might make few pearl stones more fragile than expected.

Stability
High heat can burn cultured pearls, or can cause discolouration, splitting, or cracking (unfortunately, this tends to be a common issue!)

Pearl stones can be damaged by many chemicals and various types of acids including hair sprays, perfumes, cosmetics, and oddly enough, even perspiration.

Frequently wearing pearls keeps them from being dried out.

Cleaning

What to do:

1.   For routine care, it’s best to wipe cultured pearls with a very soft, clean cloth after each wear. This will help prevent any buildup of oil or the buildup of any other substance that may have come in contact with your jewellery throughout the day.
2.   It’s safe to use warm, soapy water for occasional, thorough cleaning only when needed.
3.   Let them dry or keep them cool in any dry area before storing or wearing. If, in any case, the pearls are strung, be sure the string is completely dry before wearing.

What not to do:

Make sure that the pearls are never cleaned in an ultrasonic cleaner or steam cleaner. Ultrasonic cleaning can damage the outer layer of the pearl and may cause the pearl to fracture.  

Don’t allow your precious pearls to be submerged in water. Make sure to take them off while swimming or while engaging in water related activities including while washing up and showering.