Foggy lenses can be a frustrating problem if you need to wear glasses and a face covering at the same time.
To help limit the spread of COVID-19, the Centers for Disease Control and Prevention is recommending people wear cloth face coverings when in public settings, such as the grocery story or pharmacy, where social distancing measures are difficult to maintain. 
For the estimated 164 million American adults who wear eyeglasses, the recommendation can lead to foggy spectacles when trying to navigate the grocery store and other places.
“Foggy glasses can be more than just an annoyance, they can become a safety concern,” says Dr. Gerald Harmon, vice president of medical affairs and a family medicine physician at Tidelands Health. “It’s important people can see where they’re going to avoid hazards.”

Eyeglasses typically fog up because of temperature changes. Walk out of an air-conditioned house into a humid environment and your lenses will likely mist over because of condensation that forms on the lens surface.

Similarly, when warm moist breath escapes from the top of a facial covering during exhalation and comes into contact with the cooler lenses of eyeglasses, it can cause them to fog up. Lenses made of glass are slower to clear than those made of polycarbonate.
The good news is there are tricks to prevent lenses from fogging up when wearing a face covering.

A 2011 study published in the Annals of the Royal College of Surgeons of England suggests washing spectacles with soapy water before putting on a face covering. Shake off or gently dab the excess water and allow the glasses to air dry before putting them on.
The goal, according to the study, is the create a “thin surfactant film” that can cause the water molecules created by condensation to spread out evenly into a transparent layer. You may need to wash your glasses regularly to maintain the anti-fogging benefits of this approach.
There are also anti-fog sprays or wipes that may be used but proceed with caution to avoid eye or skin irritation, Dr. Harmon says.

Another option is to add an absorbent layer to help capture moisture before it reaches your glasses. For example, you can fold a piece of tissue paper into a rectangle and place (or attach) it where the face covering lies against your nose. Make sure, however, that you retain a tight fit.

The Tokyo Metropolitan Police Department suggests folding down the top of your face covering (though this wouldn’t apply to masks with a metal nose piece). The goal is to limit the amount of breath that reaches your glasses.

“Whatever method you choose to prevent your eyeglasses from fogging up, be sure to always wear the face covering properly,” Harmon says. “You should always keep your nose and mouth covered and avoid touching your face. And when you remove the face covering after your outing, wash it daily if it’s reusable and immediately wash your hands for 20 seconds after handling the face covering.”
Dr. Harmon says it’s also important to remember that face coverings are not a substitute for social distancing and should not be placed on young children under age 2, anyone who has trouble breathing or is unable to remove the face covering without assistance.