I had very roadworn plastic headlights on mt Dodge Caravan.
I cleaned them very carefully with 800 grit wet 'n dry paper and lots of soapy water for about 15 min, then 1000 grit paper, still with soapy water , then buffed with abrasive toothpaste. About 2 hours work and they look new. - - You can buy plastic polishing paste, but you need 2 -3 grades of it at about $18 each. Ok if your doing a lot of headlights, too much for 1 car.
Your local auto parts store will have DIY kits to restore the foggy headlights.
When its foggy or a snowstorm
Full beam lights in foggy conditions will reflect the light directly back at the driver. Dipped headlights should be used instead.
You should clean it everyday that you use it.
No, you should not use high-beam headlights at all in heavy fog.
Yes, when driving in foggy conditions you should use your headlights which allows oncoming drivers to see you at the earliest possible moment. However, for safety, you should not use your highbeams [bright] as the fog will reflect back much of the light, reducing your ability to see into [through] the fog.
You don't want to use high beams in foggy weather or snow. It actually makes it more difficult for you to see as the light reflects off the snow or fog.
It might otherwise use a copper based algaecide at the same time and that should do it.
which
You should dry clean your suit everytime your going to use it , or if you rarely use it, dry clean it every six months.
Water.
You should use dipped beams. Using high-beams simply reflects the light off the fog directly into your eyes, so causing dazzle.
It is hard, sometimes impossible, to see through foggy goggles so people don't want to use them.