When headlights fog up in a car, it can have different causes. Condensation does not always indicate damage to the lighting system. Read here how moisture can penetrate – and what you can do about it.
If the headlights on your vehicle occasionally fog up, this is not necessarily an indication of damage. Because the lighting systems are not hermetically sealed in order to enable ventilation and pressure compensation. Among other things, this ventilation system should ensure that the humidity inside the headlights regulates itself.
Nevertheless, moisture in the form of condensed water droplets can condense on the so-called lens of the headlamp – especially if the outside temperatures fluctuate significantly. This can occur depending on the time of year, for example in damp autumn, but also after visiting a car wash and cooling down in a much colder environment. Another cause of fogged headlights can be the incorrect handling of a high-pressure cleaner: the distance between the cleaner and the headlight housing should be at least 30 centimeters (1 ft), otherwise moisture can penetrate, causing the headlights to fog up.
Moisture in the headlight is not a cause for concern
In the case of headlights with an intact ventilation system, the moisture should disappear after a while, at the latest when you use the headlamps or when the weather becomes drier again. There is also no need to worry that condensation will again form in the headlights after the lights have been switched off, as the headlights may suck in moist outside air when they cool down, which then settles on the reflector and pane. But this should also disappear again in drier weather.
For example, see this lightly fogged up VW Golf headlight.
Now when you turn on the headlight and keep it on for some time. The condensation disappears.
Fogged headlights: These defects can be behind it
If the humidity inside the headlights no longer regulates itself, there may be a defect in the ventilation system. Possible causes are damaged or fallen off ventilation rubbers as well as cracks in the housing or in the cover glass. Incidentally, it is not correct that modern vehicle models suffer more often from moisture in the headlights. Since many current cars have clear-glass headlights, moisture condensation is only more noticeable than on old cars with corrugated and barely transparent cover glasses.
As a rule, there is no need to fear that rust occurs when headlights regularly fog up, because the reflectors are usually made of plastic.
How to prevent moisture
It is not always possible to prevent headlights from fogging up. However, you can reduce the likelihood of this happening by, for example, maintaining the minimum distance when washing with a pressure washer.
If you change a light bulb, be sure to close the housing properly again. If there is persistent moisture in the headlight that is not caused by damage or an assembly error, so-called silica pads can help. These have a strong water-attracting effect and are usually used in shipments of electronic devices.
However, if a larger amount of water has penetrated the headlight, only removing and drying it will help. Ideally, you drive to a workshop for this so that the sensitive systems are not damaged.