Headlight Restoration Guide
Why Do Car Headlights Turn Yellow and Cloudy?
By Clearified Headlights · 4 min read · Last updated 2026-08-01
Modern headlight lenses are polycarbonate plastic protected by a factory-applied clear coating. UV light degrades that coating, and once it fails the plastic underneath oxidizes — which is what you see as yellowing and haze.
It starts with the factory coating
Glass headlights were replaced by polycarbonate decades ago because it's lighter, tougher and can be molded into complex shapes. The trade-off is that polycarbonate reacts badly to ultraviolet light, so manufacturers apply a protective coating at the factory.
That coating has a finite life. It breaks down gradually, and it rarely breaks down evenly — which is why hazing often appears first along the top edge of the lens, the surface that catches the most direct sun.
What accelerates it
Anything that adds UV exposure, heat cycling or surface abrasion speeds up the process.
- Parking outdoors rather than in a garage
- Long summer days with sustained direct sun
- Winter road treatments and salt spray
- Highway driving that sandblasts the lens with grit
- Harsh cleaners used on the lens surface
Why it matters beyond looks
A hazy lens scatters light instead of letting it pass cleanly through the beam pattern the housing was designed to produce. Beyond the cosmetic issue, that's a noticeable change on unlit roads.