How Does
How Does a Car's Headlights Become Foggy?
Cracks and Moisture
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The biggest factor in a car's headlights becoming foggy is a crack in the headlights. Most car headlights are made of plastic, and plastic has a tendency to become pitted or cracked over time. Small cracks can allow outside moisture to pool inside the headlight; heat from the headlight bulb can cause the moisture to condense and cloud the headlight lens.
Sun Damage
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Long-term sun exposure can permanently cloud and fog up a car's headlights. The sun's ultraviolet rays penetrate deep into the plastic of a car's headlights. Over time, the plastic starts to warp and lose its luster and clarity. A hazy, foggy film then develops and obstructs a large portion of the lighting capabilities of a car's headlights.
Snow, Ice, and Sleet
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Temporary causes of headlight fogginess are snow and ice that freeze to the outside of a car's headlights. If the temperature of the outside air is cold enough, a small, thin layer of ice and/or sleet can cover the headlights and obstruct the headlight beams.
Chemicals and Abrasives
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Certain chemicals such as gasoline, kerosene and oil can mar and cloud the outer layer of a car's headlights, and abrasives such as car wax, rubbing compound, and car polish can create pitted and chipped areas on a car's headlights and create a cloudy, foggy appearance. It's advisable to take precautions in order to prevent these common automotive substances from coming in contact with a car's headlights, specifically plastic ones.
eHow Article: How Does a Car's Headlights Become Foggy?
