There are many quick fixes alleged to restore them back to new. Like using toothpaste, bug spray, or dryer sheets. It may last a couple days to a couple weeks, but it’ll always go back to foggy. This is because manufacturers have sprayed a thin clear coat over the plastic headlight lens and have now oxidized which is a dead clear coat.
The only way to truly restore headlights is to sand off the dead clear coat using multiple grits of sandpaper from 600 grit all the way up to 3000 grit. Then to finish to a like new condition using a polisher to buff out the fine scratches wet sanding left behind.
To keep them from yellowing or fogging, a wax/sealant is applied every 6 months or so. Another option we do offer is a ceramic coating for a more permanent fix.