How to defog your windshield and windows quickly

By Allstate

Last updated: November 2023

Regardless of what climate you live in, keeping the temperature comfortable inside your car may mean battling a foggy windshield and windows. If you live in a climate with cold winters, you're often using the heater to stay warm in your car, which can result in fog on the inside of your windows. In warm, humid areas, turning on the air conditioning (AC) can cause the opposite issue — fog blurring your windows from the outside. To reduce or eliminate the fog or condensation, you should try to adjust the temperature on the inside of the car to match the outside temperature as closely as possible.

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Why do windows and windshields fog up?

It has to do with temperature and the air's moisture content. On a cold day, any moisture in the air inside your car — from passengers exhaling, snow on your boots, etc. — turns to condensation when it hits air next to the windows that's below a certain temperature, called the dew point. The condensation is what makes your car's windows appear foggy. On a hot, humid day, the opposite happens, when the muggy air outside your car reaches the dew point against your windshield after it's cooled by your AC system.

Whether the fog is on the inside or the outside of your windows, any time you can't see clearly in all directions is a potential driving hazard. So, it's important to know how to make sure your windows are clear — no matter the weather.

How to defog your windows when it’s cold

When you're dealing with cold weather outside and you turn on the heat inside your car, the fog typically will start to form on the inside of your car windows and windshield.

If you're trying to defog the windows in cold weather, you want your car to continually take in the drier outside air instead of reusing the more humid air inside the vehicle. If you’re not sure whether your car has recirculation, you’ll want to look for a button on the dashboard that has an arrow going in a circle or a semi-circle. Sometimes, it will feature an icon of a car with this type of arrow inside it.

Steps to quickly defogging a cold windshield

The fastest way to defog your windshield and windows, according to Road and Track:

  1. Turn the heat on its maximum setting, because hot air can hold more moisture.
  2. Turn the AC on, which will pull the moisture from the air as it passes over the cooling coils.
  3. Turn off the recirculation button, so colder, dryer air is brought into the car.
  4. Crack your windows for a couple minutes, if possible, to help exchange the humid interior air for dryer outside air.

A more comfortable way to defog a cold windshield

If you’re trying to stay warm and snug while driving, turn on the defroster and blow warm air across the windshield to evaporate the accumulating moisture, advises Lifehacker. If your vehicle's ventilation system has a recirculate feature, turn it off. When this feature is on, your car's heat or AC reuses the air inside the car instead of continually pulling in air from outside.

How to defog your windows when it’s hot

When the temperature and moisture level outside are greater than inside the car, moisture will condense on the exterior of the car glass. Similar to when it's colder outside than the inside of your car, the goal is to change the temperature on the inside of the car to match the outside temperature.

Steps to quickly defogging a hot windshield

In this case, it means warming up the inside. Keep the following tips in mind:

  1. Use your windshield wipers. This will help get rid of the condensation until you've balanced out the temperature.
  2. Warm up the inside of your car. Turn down the AC to the lowest (least cool) setting to increase the temperature without it becoming too uncomfortable. If this doesn't work, turn the AC off completely, says Lifehacker.
  3. Leave recirculation off: As stated before, it's a good idea to turn off your car's recirculation feature to battle foggy windows so the temperature and moisture levels in your car begin to equalize with those outside.

Also, it’s not advised to wipe your windshield or windows with a cloth or fabric. Doing so can lead to streaks which could negatively impact your view in direct sunlight or when driving towards headlights, warns Consumer Reports.

Ways to prevent your windows from fogging up

Now that you have an idea of what to do when your windshield and windows fog up, let’s look at a few steps to help avoid fog form inside your car. Whether you experience foggy windows often or you’re trying to avoid defogging when you’re in a hurry, these things may help.

Keep your windshield and windows clean

As simple as this sounds, keeping the glass inside your car clean can actually help prevent fogging, explains NAPA. The dirtier your windshield and windows are, the easier it is for condensation to form on them. Clean your windshield and windows from time to time to make it harder for fog to form. NAPA recommends you use a glass cleaner specifically made for cars. If you have tint on your windows, be sure to use a product that’s ammonia-free, as it can eventually cause tint to rip or fade.

Use cat litter to prevent moisture

For times when you get fog on the inside of your windows (generally colder weather), you can use cat litter, that is designed to absorb moisture, to eliminate fog in the first place, explains Reader’s Digest. Look for cat litter that is either non-clumping or made with crystals. Once you have your litter, you can use something like an old pair of socks to put that litter in and place into your car. This should draw out moisture from the inside of your car and prevent the moisture that causes your windshield and windows to fog.

If it’s still a problem, consider an anti-fog spray

When fog in your car continues to be an issue, there are products you can use on the inside of your windshield and windows to prevent. NAPA explains that these products discourage condensation and are easy to apply. You should be able to use a paper towel or cloth with the spray and reapply it after the first application, as needed.

Trying to see through a fogged-up windshield or windows can be a driving hazard, but with these tips, you can help increase your driving safety — no matter what weather you’re driving in.