What is why do car windows fog up when you make out?

Car windows fog up during activities like making out due to a combination of factors related to temperature and humidity. Here's what's happening:

1. Humidity Increase: When two people are in a car, their breath and any perspiration increase the humidity inside the vehicle. Breathing releases moisture into the air, significantly raising the humidity level in the enclosed space.

2. Temperature Difference: The warm air inside the car, especially when people are present and engaging in physical activity like kissing, comes into contact with the cooler glass windows. This temperature difference is crucial for condensation to occur.

3. Condensation: As the warm, moist air inside the car hits the cooler windows, the air cools down as well. When the air cools, it cannot hold as much moisture, so the excess moisture condenses onto the surface of the glass, forming tiny droplets – this is what causes the fog on the windows.

4. Lack of Ventilation: Cars are relatively airtight, and during such activities, windows are often kept closed, further trapping moisture inside. Without ventilation to circulate the air and allow the excess moisture to escape, condensation is more likely to occur.

To prevent or reduce window fogging, you can crack a window to increase ventilation, use the car’s defrost setting, or turn on the air conditioning to lower humidity levels and facilitate air circulation.