Why Your Glasses Get Foggy and How to Stop It - CNET

• Get a fog-resistant coating on your lenses: Most eyeglass manufacturers offer the option to add coatings to your lenses that reduce fog and water buildup. If eyeglass fogging is a common problem for you, make sure your next pair have this feature. 
• Treat your lenses with anti-fog products: There are numerous anti-fog sprays and wipes on the market, and regular application can help keep your glasses from fogging up. 
• Use the soap-and-water trick: This is a simple alternative to buying anti-fog products. Simply wash your lenses with soap and water, then shake off the excess liquid and let the lenses dry with a thin film of soap on them. This won’t impede your vision, but it will keep fog from forming. Be sure to check with your eyeglass manufacturer to ensure the soap won’t damage any lens coatings you have.
• Make sure your glasses aren’t too tight when wearing a mask: If you do have a mask on, you don’t want your hot breath to get trapped behind your lenses. Pushing your glasses a little further down your nose and slightly over your mask can create more space and allow cool air to flow all around your glasses, preventing fog from forming, per Warby Parker.
• Seal your mask tightly around your nose: The best thing you can do while wearing a mask is to prevent your breath from hitting your glasses at all. Use the built-in flexible wire on your mask or some tape to create a snug seal around your nose and prevent air from escaping from the top of your mask.
• Keep a lens cloth with you: Sometimes, you can’t avoid your glasses fogging up, so it’s always good to have a lens cloth handy to wipe them in a punch. Make sure it’s a clean microfiber cloth that won’t scratch your lenses.