„Help, my headlights have fogged up!“ „How do I get rid of the moisture?“ These and other questions are among the one we hear most often. So it’s about time we took another long hard look at the phenomenon of fogging. That’s the name lighting experts have given to the effect you see when condensation builds up on the inside of the headlight lens.

1. What causes fogging?

All modern headlights are ventilated through small holes at the top and bottom. Ideally, they allow a gentle flow of air through the enclosure. If there was no ventilation there would be no way for the condensation ever to disappear. However, this flow of air can also allow moisture to enter the headlight. And then the same thing happens to the glass in the headlight as happens to the windows in a car when it’s cold outside and warm inside. You get a thin film of condensation.

2. Is fogging something really bad?

No. As we said, it’s just like your windows misting up. And in the same way, it disappears of its own accord in most cases. The only difference is that inside the car you can switch on a fan to get rid of the condensation quickly, whereas there is no fan in the headlight, except in those fitted with LEDs. There is a source of heat, however, which can speed up the drying process, namely the headlamp. So if you drive with your lights on you will have fewer problems with fogging. Xenon lamps produce less heat than halogen lamps so it will take a little longer for condensation to disappear from xenon headlights.

Moisture inside the headlamps is a fairly frequent occurrence. A couple of tips help to keep it under control. Picture: Osram


3. Is fogging a good reason to make a complaint?

No. Just as you wouldn’t make a formal complaint about mist-ed up windows. Once the condensation has cleared everything will be normal again and there will simply have been a short time when your headlights did not look their best.

4. Does fogging have any adverse effects on the light?

This would only be the case if the condensation extended the part of the lens through which the light from the headlamp is emitted. It would then cause the light to be unevenly distributed, resulting in glare for oncoming drivers. Generally speaking, however, condensation affects only those parts of the lens that are outside the light emission zone. Condensation particularly likes to collect at the bottom in the sharp-angled corners that designers so love to create. Ventilation has a hard job reaching these places. This is why you may even see droplets of water there.

A hair dryer can help remove stubborn deposits in head-lights. Picture: Osram


5. What can I do to prevent fogging?

It is not possible to prevent it entirely. In fact, most car manu-als say precisely that. Humid summer days and cold winter days provide ideal conditions for this phenomenon that so many car owners find unattractive. But there are a couple of ways to minimize the risk. The one most likely to succeed is to drive with your lights on all the time. If fogging still occurs then the tips we have already mentioned will help speed up the drying process.

6. The condensation won’t go away. Is there anything I can do?

Sometimes, and in certain cars, it can take quite a long time. If it’s really bad you can use a hair dryer. Obviously you have to be careful how you use it. Don’t direct it at any plastic components as there’s a risk you might dam-age them. Ideally it’ll be enough just to heat up the head-light from the outside but it’ll be quicker if you can direct the hot air into the headlight from the engine compart-ment. To do this, remove the cover as if you were about to replace a lamp.Some workshops have even started using silica pads to dry out the condensation. You’ve probably seen them in the packaging for electronic items. They can only be used once  and should not be kept per-manently in the headlight. A couple of hours with the car stationary should be enough. Don’t put silica pads in the reflectors, however, because they can easily get stuck there.

7. Can I improve the ventilation for the headlights, for example by making more holes or by leaving the cover off at the back?

No. In most cases this would just make the problem worse because the flow of air through the enclosure would be compromised. There would also be a much greater risk of dirt getting into the headlights. And dirt doesn’t disappear by itself. There are some headlights that are not exactly well designed, and some that are installed with less than optimum ventilation. Perhaps that is the reason why some manufacturers have issued instructions on how to install additional tubes to improve the exchange of air. Changes to the ventilation holes also fall into this category. It’s best if you ask your official dealer.

8. Should I try to open up the headlight to remove the moisture?

No way! The risk of breaking something far outweighs the minor irritation of the headlights not looking their best. And anyway the adhesive between the lens and the en-closure is really strong. You may have come across the „oven trick“. This damages the internals and may distort the enclosure.

9. I gave the engine a wash. Now there are gray smears in the headlights.

This is residue from the detergent used. The high-power jets in the car wash forced some of it into the headlights. Unlike pure water that has condensed from humidity in the air (in other words fogging), detergent deposits will not disappear of their own accord. So never aim a jet of water directly at a headlight. Not even from the outside.

10. There‘ a few centimeters of water in my headlights.

That’s not fogging. In most cases this is caused by a small crack or a broken seal. In a few cases it may be because a hole is blocked up. There are various reasons for this. Insects have been found in the holes. And dirt is a com-mon cause. Workshop mechanics have even come across clever people who have stopped up the holes with seal-ant, preventing water from draining out.

When it comes to fogging and moisture in headlights you can do more harm than good. So our advice is to ignore it in the first instance.

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  • I have been told that this is an offence and could be a reason to fail an MOT. Also that should the moisture build up it could knock out all the electrics. Is this true?

    • Dear P Miller,
      thanks for your request. All electronics are sealed against water and moisture. The same applies to most of the more simple electrical circuits. So, moisture will not destroy it. Of course, all technical devices work better and stay in better condition as ling when kept dry.
      Best regards,
      your carlightblog team

  • Hello. My car has a little condensation in the headlights. I believe it is because of the cold weather and the rain. Will they eventually clear up? Can I send you photos to aid in determining weather or not they will clear up?

    • Dear Harry Singh,
      Well, cold weather and high humidity are common reasons for fogged headlamps. As pointed out in our post the condensation usually disappears by itself as soon as the weather conditions improve. Using the headlights very often and preferably always shortens the time to remove condensation as the bulbs warm up the interior of the headlamps. If this does not help it can be beneficially to check the ventilation holes or rubber nozzles. They must not be clogged. Of course, no parts of the headlamp should be cracked or otherwise damaged.
      Best regards,
      your carlightblog team

  • I had this on a Honda Accord and used a hair dryer with the rear headlight cover removed. The perspex crazed quite quickly. I found that a better solution was waiting for reasonably dry weather. Remove the rear cover and drive it around for a day. The heat from the engine bay evaporates the moisture through the open headlight. If possible, reverse then lubricate the rubber o ring. Refit the cover. It didn’t fog up again.

    • Dear Jalen, yes, a defective or wrong fitted rear cover of a headlamp can be the reason for moisture or fogging. The internal ventilation is disturbed if air can escape from the headlamp or enter it thru the cover and not via the channels provided by the design. Please make sure that the cover is not damaged. Usually there is some kind of seal inside the cover. In most cases it is a rubber seal. It must be complete and undamaged. Take care that the rear cover is fittet properly. Best regards, your OSRAM Automotive Team.

  • condensation on the lens, the water droplets can refract the light from both main and dipped beam causing the beam to become a dazzle hazard and a MOT failure.

  • It is truly a nice and useful piece of information. I?¦m happy that you just shared this helpful info with us. Please keep us up to date like this. Thanks for sharing.

  • My headlight look like a layer of dust has gathered more than moisture. How do I get rid of that? Do I have to change the entire light system?

    • Hey Glen, sounds like there’s to much moisture in your headlight. Please get in touch with your local workshop. Best regards, your OSRAM Automotive-Team

  • My headlights had some condensation on it and caused my right beem light to dip. If i dry it out, will it still work or do i have to replace my headlights?

    • The full light and its distribution will be restored once the condensation is dried out. Just follow our tips. Best regards, your OSRAM Automotive-Team

  • I had a bulb changed by Halfords in my Fiesta. After a couple of days I noticed the headlight went cloudy, full of damp. Guess what, the cause was the stupid boy failed to replace the plastic back cover disc, so I got a back cover from the dealer, after allowing it to dry out with the lights on, I put the back cover on, now no more condensation. If you have this problem, check if the cover is missing.