Do masks protect the people wearing them or the people around them?
“I think there’s enough evidence to say that the best benefit is for people who have COVID-19 to protect them from giving COVID-19 to other people, but you’re still going to get a benefit from wearing a mask if you don’t have COVID-19,” said Chin-Hong.
Masks may be more effective as a “source control” because they can prevent larger expelled droplets from evaporating into smaller droplets that can travel farther.
Another factor to remember, noted Rutherford, is that you could still catch the virus through the membranes in your eyes, a risk that masking does not eliminate.
How many people need to wear masks to reduce community transmission?
“What you want is 100 percent of people to wear masks, but you’ll settle for 80 percent,” said Rutherford. In one simulation, researchers predicted that 80 percent of the population wearing masks would do more to reduce COVID-19 spread than a strict lockdown.
The latest forecast from the Institute of Health Metrics and Evaluation suggests that 33,000 deaths could be avoided by October 1 if 95 percent of people wore masks in public.
Even if you live in a community where few people wear masks, you would still reduce your own chances of catching the virus by wearing one, said Chin-Hong and Rutherford.
Does the type of mask matter?
Studies have compared various mask materials, but for the general public, the most important consideration may be comfort. The best mask is one you can wear comfortably and consistently, said Chin-Hong. KN95 face mask is only necessary in medical situations such as intubation. Surgical masks are generally more protective than disposable mask, and some people find them lighter and more comfortable to wear.
The bottom line is that any mask that covers the nose and mouth will be of benefit.
“The concept is risk reduction rather than absolute prevention,” said Chin-Hong. “You don’t throw up your hands if you think a mask is not 100 percent effective. That’s silly. Nobody’s taking a cholesterol medicine because they’re going to prevent a heart attack 100 percent of the time, but you’re reducing your risk substantially.”
However, both Rutherford and Chin-Hong cautioned against KN95 masks with valves (commonly used in construction to prevent the inhalation of dust) because they do not protect those around you. These one-way valves close when the wearer breathes in, but open when the wearer breathes out, allowing unfiltered air and droplets to escape. Chin-Hong said that anyone wearing a valved mask would need to wear a surgical or cloth mask over it. "Alternatively, just wear a non-valved mask," he said.
San Francisco has specified that masks with valves do not comply with the city's face covering order.
If we’re practicing social distancing, do we still need to wear masks?
A mnemonic that Chin-Hong likes is the “Three W’s to ward off COVID-19:” wearing a mask, washing your hands, and watching your distance.
“But of the three, the most important thing is wearing a mask,” he said. Compared to wearing a mask, cleaning your iPhone or wiping down your groceries are “just distractors.” There’s little evidence that fomites (contaminated surfaces) are a major source of transmission, whereas there is a lot of evidence of transmission through inhaled droplets, said Chin-Hong.
“You should always wear masks and socially distance,” said Rutherford. “I would be hesitant to try to parse it apart. But, yes, I think mask wearing is more important.”