Why Car Windows Fog Up?


When you get in your car in the winter, you may notice that after some time, the windows will begin to fog up. They may even fog up to the point where you can no longer see the road, at which point it becomes dangerous. In order to understand how to prevent foggy windows, we must first understand why they occur.

Your car windows fog up when there’s a difference in temperature between the inside of the car and the outside, with the outside being colder. This temperature difference changes the air humidity levels and can cause moisture to condensate on your car’s windows.

In the rest of this article, I’ll go over how exactly the temperature difference causes fogginess. After that, I’ll quickly go over some easy ways to keep the fogginess from occurring. 

What Causes Car Windows To Fog?

Windows begin to fog up because the change in air temperature makes it so the air can hold less moisture. Cold air holds less moisture than hot air, so when the air hits the cold windshield and windows, it can begin to condensate and make your windows go foggy.

Think about when you go outside during the winter, and you breathe into the cold air. There’s typically fog, but why is that? The air that you breathe out is typically at 100% humidity. After all, it just finished traveling through your airways. It’s also hot, which allows it to hold all of that humidity.

When your breath hits the cold air, it’ll begin to condensate into tiny droplets of water. That’s the fog that you’ll see, simply tiny droplets of the moisture that your breath was holding. Cold air can’t hold near as much moisture as hot water can, so when your breath hits the cold air, any water that it’s carrying will be forced out when your breath hits the cold air.

The same thing occurs when you have a significant temperature difference between the exterior and interior of your car. The air outside the car is colder and drier. You’re breathing into the interior of the car, which is creating heated, moist air. The air from outside will chill the glass of the windows and windshield. Then when the heated, moisture-filled air from the inside hits the glass, it’ll cool down, which lessens the amount of water vapor it can carry.

This will cause the water vapor to accumulate on the glass in tiny droplets. This creates the foggy window appearance.

Read: How to Defog Car Windows in Rain Without AC

Fogging During Warmer Conditions

Although the most common time for foggy windows to occur is during cold weather, it’s also possible to have an issue with foggy windows when the temperature outside is hotter. They’ll just be occurring in reverse. 

Since the air outside has more moisture than the air conditioning cooled glass, water droplets will begin to accumulate. This is mostly common in areas that are naturally very humid or shortly before or after it has rained. 

How To Get Rid of Foggy Car Windows in Cold Weather?

Foggy windows are actually extremely dangerous. They can significantly impact your ability to see the road, so it’s important to know how to correct it should they begin to fog up.

Use the Defog Button

The majority of vehicles nowadays have a defog button that you can use. This button will heat up the air around your windshield to raise its temperature. This will help to evaporate the water and also prevent more condensation from accumulating on the glass. 

The benefit to using this button is that it’ll heat up the glass to remove the fog without drastically changing the temperature of the interior of the car. The downside to this is that not all cars come with them and it can also take quite some time to work. If you’re already driving, this could mean that you have to pull over and wait several minutes until the windows actually defog.

Read: Why Your Car Won’t Defrost Windows

Turn the Heat Up

The second option is to simply turn the heat all the way up in your car. This will raise the temperature of the car enough that it should heat the glass and help to get rid of the condensation. 

The downside to this is that, of course, it’s going to heat up the interior of your car quite a bit. If you don’t want to get any warmer, this can leave you sweating. The benefit to using this method is that it’ll usually clear the fog from your glass much faster than just the defog button would.

If you want the fastest possible, then you can combine both the regular heat and the de-fog which will be the fastest way to heat up the glass of the car.

Crack the Windows

If you don’t have time to stop and you need to fix the problem super quickly, then cracking the windows, or completely opening them, could be the solution.

Cracking the windows will change the interior temperature to match the exterior, which will prevent anymore fog from forming. The moisture that’s already on the windows will take some time to go away, but at least with this method, it shouldn’t get any worse. 

Read: Why Car Windows Won’t Stay Up?

Apply Shaving Cream

One more fun hack for fixing foggy windows in cold weather is applying shaving cream to the inside of your windows.

Think of as a kid when you go to the pool and your goggles start fogging up everyone tells you to spit in them. The spit works to create a film on the surface of the glass so the water droplets can’t accumulate there. 

The shaving cream trick works in the same way. You’ll apply it to the inside surfaces of your windows, let it sit for a couple of minutes, then wipe it off with a paper towel. It should leave enough of a coating on the surface that it’ll prevent water droplets from accumulating while still allowing you to see through it. 

This is a good one if foggy windows are a chronic problem for your car and your heating or air conditioning system isn’t currently functioning. It should prevent fogginess even if there’s a significant temperature difference between the inside and the outside.

Read: How Much Is an Inspection for a Car? 

How To Get Rid of Foggy Car Windows in Warm Weather?

As previously mentioned, it’s entirely possible for your windows to fog up during warmer months. Here are a few simple ways how you can combat this problem.

Use the Windshield Wipers

If you’re having issues with fog accumulating on the outside of your windows during hot weather the best thing you can do is use your windshield wipers. Since the moisture is on the outside of your glass the windshield wipers are able to simply wipe the water away and you should be able to see once it has been removed. 

The only real downside to using this method is that you’ll need to use it continuously until the outside humidity decreases.

Read: How Much Does It Cost to Replace a Windshield Without Insurance?

Turn on Air Recirculation

Another thing that you can try is turning on air recirculation in your car. This means that instead of pulling in fresh air from outside the car your car will begin to recirculate the air that’s already in there.

Doing this can help the car to gradually heat up and let the interior air increase in moisture until it’s closer to the outside air.

Keep in mind that this method will likely work very slowly so if you need an immediate solution, this isn’t the best option for you and it’s better to use one of the more drastic tactics.


Foggy windows are caused by moisture accumulating on the glass when there’s a significant temperature difference on the two environments. This most commonly occurs in cold weather but can also occur in hot weather when the air holds high levels of moisture.

The best way to fix this problem is to minimize the temperature difference between the two environments. You can do so by changing the temperature through the temperature control settings or by simply opening the windows. You can also physically remove the moisture using windshield wipers if the problem area is located on the outside.

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