Glasses fog up because they are at a lower temperature than the heat emitted by our faces. Tiny water droplets are formed by condensation on the surface of the eyeglass lenses. This happen often under cold and humid weather conditions. It can also can be a safety issue, since it limits your ability to see until the fog clears. Lens fogging can be especially dangerous for police officers and other first responders to emergency situations. Fogged up lenses is undoubtedly a nuisance for eyeglass wearers.