Anti-fog glasses

Why do eyeglasses get fogged in daily life where we are forced to wear masks?

Eyeglass lenses get fogged due to “dew formation.”
When the moisture contained in expired air comes into contact with the eyeglass lenses and is cooled, it forms dew. The lenses lose clarity due to diffusely reflected light and look fogged.
In particular, eyeglass lenses are likely to get fogged in the wintertime when temperature wide varies, and in air-conditioned rooms or trains in the humid rainy season.

Countermeasures / Improvements

• Use eyeglass lenses less likely to get fogged (anti-fog lenses).
• Use an anti-fog spray or a dedicated eyeglass cloth.
• Fogging can be reduced to some extent by taking some measure to prevent the expired air leaking from the mask from coming into contact with the lenses.
  *Note that the effect of an anti-fog agent depends on the environment where it is used.