Why do headlights turn yellow and cloudy?

Modern headlights are made from polycarbonate — a tough, impact-resistant plastic that replaced glass decades ago. Polycarbonate is strong, but it's also vulnerable to ultraviolet light. To slow that damage, manufacturers apply a thin factory UV coating to the outside of every lens.

That coating is what fails first. Years of sun, road heat, and washer chemicals wear it down until the raw plastic underneath is exposed. Once that happens, oxidation sets in and the surface turns hazy, yellow, or milky.

Polishing a lens without addressing the coating only buys a few weeks of clarity. A proper restoration removes the failed layer, refines the plastic in stages, and seals it again so the clarity lasts.

If your headlights look tired but the housing itself is intact, restoration is almost always the smarter choice — you keep the original assembly and get back the light output you paid for when the vehicle was new.