​​​​​​​Oxidation is a naturally occurring event. It is a buildup of loose oxygen electrons that are attracted to the surface of the headlight.  These electrons are drawn to the surface of the lens in concentrated amounts when current is passing through the headlight. These electrons will build up on the surface until no light can come through. In the process they create an absorbent surface layer that will trap road debris such as gas and oil. These additional contaminants can turn the oxygenated surface from white to yellow to brown. Environment and vehicle maintenance has a large part to do with how fast this will happen.