Most likely this has happened to you; you jump into your car and after you’ve been driving for a few minutes, your windows begin to fog up. First thing you say to yourself is, “Why do bad things happen to good people?”. But you really might be wondering why do windshields fog up like this? Well, there can actually be a variety of reasons why your windshield would fog including:

  • Humidity

    When there’s humidity in the car, it causes a buildup in water that turns into water vapor. We breathe the humid air and this air comes out from inside our body or off of it. Windshield fog tends to be more of a problem when there is more than one person in the car due to there being more breathing.

  • Heat

     A higher temperature is what happens when molecules are moving, and more moisture is held with warm air than cold air. However, this is not the result of a chemical reaction. The molecules aren’t holding on to water molecules. Water becomes more gas-like when it’s warmer than it does a liquid. And, there’s more space between each molecule with a warmer air therefore, the water molecules can fit into this space.

  • Condensation

    Moist, warm air condenses when it hits your car’s cold windshield, causing condensation. This usually happens when you’re driving first thing in the early morning. This is also why on those humid, warm days when you have your car air conditioner running for dear life, you’ll see condensation form at the windshield’s base where it meets the cool air.

To clear away the fog on your windshield you can dry the air out by running your air conditioner or heater. This is usually your best option and works well when the outside temperatures are above freezing and damp, wet humans getting into the car causes the fog. Other options include putting on your defroster on a high setting, setting the temperature to hot, and cracking your windows.