Do pearls fade over a period of time?

Because there are so many different types of pearls and treatments available for pearls, it is not really possible to say for sure. You need to take them in to a certified pearl dealer for inspection and cleaning.

Pearls are composed of calcium carbonate, which is both soft and soluble in acid. Acidic secretions from the skin can etch the pearls’ surface over time, reducing their luster. Also, they’re easily scratched; minute scratches can accumulate to produce a haze over the surface.

As harp says, body moisture, lotions, hairsprays and soaps can damage the lustre of pearls but otherwise they are pretty resilient, especially natural (unseeded) pearls. If you have strung & knotted pearls then it’s a good idea to have them restrung on fresh silk every 5yrs or so because the silk also becomes damaged and brittle with time and wear. I like to give mine a wash now and then with mild soap and buffed with an old cotton t-shirt.