What Causes Fog Inside Headlights?
2 Answers
The reasons for fog inside headlights: 1. Temperature difference causing fog: There is a vent tube on the rear cover of the headlight. Hot expanding gas is discharged through this channel, which can allow moisture to enter the vent tube, resulting in slight fogging. This phenomenon usually occurs in winter, rainy seasons, or foggy weather; 2. Washing the car or driving through water causing fog: Improper car washing or driving through water can lead to fogging. When cleaning the engine, use a wet towel instead of directly spraying with a high-pressure water gun. Methods to remove fog inside headlights: If caused by temperature difference or moisture, turning on the low or high beams for about 10 minutes will gradually dissipate the fog inside the headlights. The moisture inside will quickly evaporate during normal use of the headlights or under sunlight. Never use baking methods to remove fog from headlights to avoid damaging them.
I've researched this before. Car headlight fogging is mainly a natural phenomenon caused by temperature differences. When the internal temperature of the headlight is lower than the external temperature, moisture in the air condenses on the inner surface of the lens, forming fog. This is especially common in humid weather or immediately after car washing. Headlights are typically designed with tiny vent holes to alleviate this issue. If the fog appears briefly and dissipates quickly, it's normal and nothing to worry about. However, if the fog persists for a long time or even accumulates water, it may indicate aging or cracks in the lens or sealing gasket. Damaged seals allow external moisture to enter, which over time can affect light brightness and even shorten bulb lifespan. I recommend avoiding turning on the lights immediately after washing the car during autumn and winter seasons, and waiting until the vehicle temperature stabilizes to reduce the chance of fogging. Regularly inspecting the headlight housing and edge seals is also crucial. Small cracks should be temporarily patched with tape until professional repairs can be made.
