Why car windows are fogging up inside and how to fix

Car windows that fog up are not an uncommon issue, especially in winter and in high humidity. It is worth figuring out why this is happening before you start to fix the problem because it can create a dangerous inconvenience, the fact that you will not have good visibility when driving which leads to a high risk of an accident.

It is important to understand that the quality of windows installed on cars is different. Depending on the make and model, the big difference can be with what substances the windows are treated and if they have the feature of being electrically heated, this can be enough to see a fogging window rarely.

If the car has electrical heating for the windscreen, it will help quickly dry the windows without turning on the heater or AC. Also, in winter, this feature will quickly clear the glass itself from ice and snow. 

You can add this option to “must-have” when you want to buy a car, however, newer cars already have this option as standard.

What causes the car windows to fog up?

As I said above, most often you will notice steam on the car windows in winter when it rains when it is foggy, and in conditions of high humidity.

Visibility in these conditions is usually poor, and the risk of an accident significantly increases, because, usually, all windows will fog up. It also happens that the reason for the fogged-up windows is not only the weather. 

In any case, you need to know what to do in this situation and what to do to keep the windows from sweating. Let’s see what are the causes.

Colder temperatures

In winter, the car windows fog up because condensation forms as a result of the interaction of warm air inside the cabin and cold air outside. This condensation accumulates on the windows, causing them to fog up.

High humidity

Another common cause is when it is raining. This happens because the humidity in the cabin rises significantly. Moreover, moisture begins to actively evaporate from the driver or passenger’s wet clothes, as well as from wet mats after the heater is turned on.

Problems with the cabin filter

If the cabin filter has not been changed for a while it will have dirt and debris, causing it to have a hard time adding air from the outside.

Also, its defects, model mismatch, or errors in the installation of the cabin filter will cause it to not absorb moisture and dust properly, and the result will be misted windows.

Air recirculation is turned on

Most cars nowadays have the option to recirculate the air from the cabin. This option blocks fresh air from the outside from entering the interior. In certain situations, this feature is useful, as it avoids dust and unpleasant odors from the outside to get in the car.

The interior can be warmed up or cooled down faster by turning on recirculation, but this also will cause the windows to fog up. As a simple solution, just turn off the recirculation.

There are some cases where this feature has faults such as a jammed valve and does not allow outside air to enter the cabin, but these situations are rare.

Coolant leaks

If the heater radiator or any branch pipe leaks, the coolant may enter the cabin and evaporate. This is why the moisture found on the windows can be oily.

In any case, if you find leaks on the driver’s side and the passenger side, you need to figure out the cause quickly, because there could be serious malfunctions in the cooling system.


Alcohol vapors that are exhaled by a person who has been drinking alcohol will cause the car windows to fog up.

How to prevent car windows from fogging up?

The first thing you should do is to know the exact cause why car windows fog up and after that to fix it. Of course, you can wipe the glass whenever that happens, but this only consumes time and does not resolve the issue, it will only allow you to get rid of the consequences.

You can also turn on the car’s ventilation system to dry out the windows, but as a disadvantage, you will have to wait a long time for the motor to warm up, especially at a cold start. 

For better results, you can turn on the AC which will give faster results in removing the moisture, but as a downside, fuel consumption increases, and the resource of the AC decreases.

I have composed a list below of tips that are efficient for preventing car windows from fogging. But before using them you should wipe the windows from the inside using a paper towel or dry cloth to remove the moisture and dirt.

  • Lemon. Cut it in half and wipe the glass with it. Fogging will stop and you will also get a pleasant smell in the cabin;
  • Soap. It doesn’t matter what type of soar it is. Just apply it to the surfaces of the windows, then wipe the entire area with a dry cloth and then with a paper towel. Here you can also use shaving foam, it works the same way, but thanks to its semi-liquid state, the process is faster
  • Regular salt. Rub the glass surface with it, and as a preventive measure, place the salt in small bags on the center console or dashboard;
  • Alcohol solution in glycerin in a ratio of 1:20. Treat the surfaces with a clean cloth or a sprayer, then wipe the glass.

Moreover, to prevent the windows from fogging, you should periodically check the car’s ventilation system, check the heater and fan, etc, and, most importantly, you need to change the cabin filter on time. Also, don’t forget to turn off the recirculation.

Another way to prevent windows from fogging is to stick a special film. Such a film also has the property of preventing moisture accumulation. 

An anti-fogging car glass spray is also a great solution. The composition is applied to windows that were previously washed, dried, and degreased. In practice, the solution is effective, but one application is enough for only 10-15 days.

You can also do an anti-fogging solution yourself by mixing ethyl alcohol with glycerin. The ratio is 20: 1, where 1 is glycerin. The mixture is then placed in a spray bottle for ease of application.

How to properly remove moisture from the windows inside the car

  • If it’s winter, you first need to remove the ice and snow from the windshield and side windows. As long as the ice lies on the glass, it will sweat from the inside, even with the intense blowing of warm air.
  • Then, to clean the windows from fogging, no one should be in the car. Turn on the heater and wait for it to blow warm air.
  • Next, turn off the recirculation if it’s on, to allow fresh air to flow from outside. By adjusting the air deflectors, try to direct air towards the windows.
  • If it is relatively warm outside and it is raining, moisture is better removed by turning on the AC.
  • At the same time, it is not necessary to warm up the engine, since the temperature of the air blown onto the glass does not have a strong effect in this case. 
  • After the windows have been cleaned, you can turn on recirculation so that the windows do not sweat further during the trip. However, increased humidity in the cabin can cause the windows to fog up again. In this case, you need to try other options.
  • Regarding the rear window, things are easy, just turn on the heating.


As you can see, to make sure that car windows won’t fog up inside due to weather conditions an important aspect is to ensure the most efficient ventilation in the cabin. Sometimes instead of waiting for the heater to dry out the moisture, it is better to slightly open the windows.

The cabin filter must be the right one and also changed on time. If you are unsure about its quality, it is better to buy a more expensive carbon filter than cheap aftermarket ones. Also, the filter itself must be installed correctly.

Also, do not leave wet things, like shoes, jackets, etc. inside the car, as it dries, moisture will settle on the windows. It is also recommended to drain the water and properly wipe down the rubber mats. Fabric mats must be removed from the vehicle and dried separately.

If the car has been in high humidity conditions for a long time, it is necessary to dry the entire interior. This can be done by leaving the car in a warm garage or parking lot for several days with the windows slightly open.

If the windows are fogging up while driving and the heater and/or AC cannot cope with clearing the windows, it is recommended to drive with the side windows open. Also, if it is hot in the cabin and cold and humid outside, it is better to open all doors for at least 5 minutes after driving to get fresh air into the car.

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