Why Do Car Headlights Turn Yellow?
2 Answers
Car headlights are made of polycarbonate plastic, which is prone to oxidation buildup. When sunlight shines on the headlights, it causes the pores in the polycarbonate plastic on the surface to expand, accelerating oxidation and yellowing inside the headlights. At the same time, dirt and debris adhere to the outer surface of the headlights. Wipe the headlights with a soft cloth: Regularly wiping the headlights lightly with a cloth to remove dust can prevent stubborn dirt buildup. During the cleaning process, avoid using rough cloths or applying excessive force, as the plastic surface of the headlights can easily be scratched. Once scratches appear on the headlight surface, they can trap dirt, making it difficult to clean and potentially affecting the lighting performance. Clean the headlights with soapy water: Soapy water is a mild alkaline substance that is non-corrosive, gentle, and highly effective for cleaning headlights. The materials needed include soap, a basin, a magic eraser sponge, and water.
I found that the main reason car headlights turn yellow is prolonged exposure to ultraviolet (UV) rays, especially for older cars parked outdoors for over a decade. UV radiation causes the plastic covers of the headlights to oxidize gradually, much like how plastic toys discolor under sunlight. Over time, dust and impurities from rainwater accumulate on the surface, combined with erosion from acidic substances in the air, making the headlights appear foggy. I experienced this issue with my old car—yellowed headlight covers significantly reduced visibility at night, as the light output was obstructed. To prevent this, it’s best to regularly clean the covers with a soft cloth or use a car cover to block sunlight. Otherwise, brightness diminishes noticeably. If the yellowing is severe, professional polishing or restoration at a repair shop is an option, though it may cost a bit. Overall, proper maintenance can delay this issue.
