Center caps turned "milky"

[Bob O]

What the heck?? I washed the car Sat since it was about 60 around here and when I was doing the wheels I noticed that all four center caps had fogged over. I tried to clean them but it looks like it's not something just on the surface but has faded or something. The car's been in the garage for a month or so and the last time i washed it the caps were fine. There isn't anything in the garage that I can think of that would have caused this issue. And there doesn't seem to be anything else on the car that's affected adversly. Is it just age? Or somethig else perhaps? I think I know the answer to this but I'll ask anyway....any hope of bringing these back to life or am I stuck with getting new center caps?

Thanks for your help
Bob