Oxidation - Over time acrylic headlights will oxidize when exposed to the sun. All headlights come with a clear coat to try and slow the process, but with time, the suns harsh UV rays turn the plastic yellow.
But don't fear!
This can be fixed by a professional car detailer.
Getting headlights on a car restored both increases visibility at night and the potential sell price of the vehicle.
Here's a video of us exposing our secrets and revealing how we restore headlights to a better-than-new finish.