Mirrors fog up when warm, moisture-laden air contacts the cooler glass surface, causing water vapor to condense into tiny droplets that scatter light and create a cloudy appearance. This common bathroom phenomenon occurs because shower steam significantly increases air humidity while the mirror typically remains at room temperature. The temperature differential triggers condensation at the dew point—when air can no longer hold its moisture content. To prevent mirror fogging, you can: apply anti-fog solutions containing surfactants that prevent water droplet formation; install a mirror defogger that warms the glass surface; improve bathroom ventilation; or temporarily warm the mirror before showering by running a hairdryer over it or wiping with warm water.
