"Pearls on last and off first".
Pearls are porous so absorb chemicals such as perfume, hairspray, lotions, sweat etc. If not cleaned off these contaminates will affect the lustre and eventually dull/discolour the pearl. As a gem they are relatively soft so will scratch against hard items.
Simple Care Instructions
Clean your pearls regularly to remove sweat and other build up.
To clean, wipe with a soft damp cloth and then dry with same.
If wearing your pearls often then occasionally clean gently in some warm soapy water and dry well.
Pearls strung on silk should be restrung every 12 months.
Store your pearls flat and away from other jewellery.