A bathroom mirror fogs up during a shower due to condensation. Hot steam from the shower comes into contact with the cooler surface of the mirror, causing moisture to collect. To prevent fogging, use a bathroom exhaust fan, apply anti-fog coatings, or wipe the mirror with a solution of water and vinegar.

Mirror fogging is caused by condensation from steam. Using exhaust fans or anti-fog treatments can mitigate this issue and keep your mirror clear during and after showers.