Why Headlights Turn Yellow (And How To Fix Them)
If your headlights look yellow, cloudy or foggy, you're not alone — virtually every modern car suffers the same fate. Here's the science behind why, and what you can actually do about it.
The polycarbonate problem
Until the early 1980s, headlights were sealed glass units. Glass was heavy, expensive, and limited in shape. The auto industry switched to polycarbonate plastic, which is lighter, cheaper, more impact-resistant, and lets designers create the sleek wraparound shapes we see today.
But polycarbonate has one major weakness: ultraviolet light destroys it. To compensate, manufacturers apply a thin protective UV-resistant clearcoat to the outside of every lens at the factory.
Why the factory coating fails
That factory coating is the first thing to go. Years of direct sunlight, road heat, headlight bulb heat from the inside, salt air, automotive chemicals, sprinkler water, sand and grit gradually break down the clearcoat. Once it's gone, UV reaches the bare polycarbonate underneath and oxidation begins — the same chemical reaction that yellows old plastic patio furniture.
In Southern California — San Diego, Temecula, the Inland Empire — UV exposure is especially intense. Most vehicles here start showing oxidation within 3–5 years.
What restoration actually does
Cleaning the outside of an oxidized headlight does nothing. The damage is in the plastic itself. Professional restoration removes the failed UV layer and the top microns of oxidized polycarbonate through multi-grit wet sanding, then polishes the lens back to optical clarity, then seals it with a fresh industrial-grade UV ceramic coating.
Done correctly, the restored lens is optically equivalent to new — and protected against the very damage that caused the problem in the first place.
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