What Causes Fogging on Car Side Windows Obstructing Rearview Mirror Visibility?

[Derek]

This phenomenon generally occurs due to high humidity inside the vehicle coupled with low external temperatures, making it more frequent during spring, autumn, and winter seasons, while being rare in summer. Simply prepare a highly absorbent towel and gently wipe it off. Below are some methods to remove window fogging: 1. Open windows: Slightly opening windows creates air convection, using negative pressure to draw out fog. If equipped, open the sunroof and utilize its rear tilt function for rapid air exhaust. 2. Use the car's front defroster mode, which can quickly restore window clarity. 3. Apply anti-fog products: Many commercial anti-fog sprays work effectively when pre-applied on glass surfaces.

[OJayce]

This is mainly caused by the large temperature difference between the inside and outside of the car. When it's cold outside and warm inside, the moisture in the car easily condenses on the glass, forming fog. Especially on rainy days or when the air is humid, closing the windows traps the moisture from breathing inside, causing the glass to fog up and block the rearview mirror's visibility. Another reason is improper use of the air conditioning system, such as setting the fan speed too low or not switching to defog mode, which prevents moisture from being effectively expelled. In some cars, a dirty air filter can also reduce dehumidification efficiency. To solve this, turn on the air conditioning and use cold or hot air to blow against the windshield while pressing the defog button to quickly clear the fog. Remember not to wipe the glass while driving; pull over to a safe spot first. Regularly cleaning the car's air conditioning system can also prevent such issues, as frequent fogging can seriously affect driving safety.

[KyleMarie]

From my personal driving experience, fogging on the left and right windows is mainly caused by excessive humidity inside the car. For example, in winter when the heater is turned up high and the windows are tightly closed, the moisture from breathing condenses on the glass, obscuring the rearview mirrors and making it impossible to see. Also, on days with rapid weather changes, such as sunny days after rain, the large temperature difference between the inside and outside easily causes condensation. When defogging, don’t panic. First, set the air conditioning to the defrost mode, turn on a bit of external circulation, and increase the fan speed by a few notches—the fog will gradually dissipate. If there’s an issue with the air conditioning system, like a non-functioning fan or blocked ducts, it’s necessary to have it repaired. Keeping the interior dry is crucial; placing some moisture absorbers on the seats can prevent humidity buildup. Before long trips, always check if the defogging function is working properly. Otherwise, not being able to see the mirrors when changing lanes or turning is very dangerous and can easily lead to accidents.

[StNicole]

With children frequently riding in the car, I've noticed that fogging on the side windows is usually caused by excessive humidity inside the vehicle. This is especially common in winter when turning on the heater leads to window fogging, as breath and sweat vapor can't dissipate. This condensation sticking to the mirrors becomes particularly annoying when the rearview mirror gets completely blurred. Causes may include poor vehicle sealing allowing moisture ingress or the air conditioning not being set to the defog position. A simple solution is to stop the car, open the windows for a few minutes to ventilate, and the fog will disappear as the humidity dissipates. For daily prevention, it's advisable to use the external air circulation mode more often than the internal one. Keeping a clean cloth in the car for quick wipes can also help, but avoid doing this while driving—safety first.