Fogless mirrors are made for men who need to shave while they are in the shower. They are designed to resist fogging so a man can shave his face while showering. With a foggy mirror, he may miss a spot or accidentally cut himself. Even though they are fogless, these mirrors do begin to fog up over time; however, a proper cleaning will restore them.
Dampen a rag and use it to wipe down your mirror. This will remove any dust or light dirt on the mirror.
Spray some WD-40 on a paper towel and work it in to your mirror. Get the sides as well as the middle of the mirror.
Use another paper towel to wipe any excess WD-40 off. Make sure there are no streaks that would leave the mirror looking unclean.
Let the mirror dry. It will now be clean and fogless again.