White House officials announced recently that they will give out 400 million free N95 masks around the country — that’s three per adult — starting as soon as this week and continuing into February. While some details of the plan still haven’t been announced, here’s what we know, and what experts have to say about masking in the age of omicron.

What is the White House’s plan to distribute free N95 masks?

The White House tweeted last Wednesday that the administration will make available 400 million N95 masks for the public. They will be available to be picked up at “tens of thousands of local pharmacies and health centers,” the White House said.

Quoting an unnamed administration official, the Washington Post reported that the program could begin as early as this week, and should be in full swing by early February. NPR reported that the masks will be distributed from pharmacies that are part of the federal retail pharmacy program, a group of major pharmacies that includes CVS, Walgreens, and Rite Aid.

Adults will be able to get three free masks for themselves; masks won’t be available for children yet, but the administration official told the Post that the White House “anticipates making additional, high-quality masks for children available in the near future.”

Where are the masks from, and why are they available now?

The masks are from the Strategic National Stockpile, and are certified by the National Institute for Occupational Safety and Health (NIOSH), said Aparna Kumar, a psychiatric mental health nurse practitioner at Jefferson University Hospital, and the chief community officer at Dear Pandemic, an educational website about the COVID-19 pandemic.

“These supplies were stockpiled for emergency times, intended mostly for health-care settings,” Kumar said.

In the early days of the pandemic, N95s were in extremely short supply, and health officials stressed that they should be reserved for health-care workers. Now, with those shortages long since eased, it’s possible to distribute those masks to the public, said physician Marcus Schabacker, the president and CEO of the health-care safety nonprofit ECRI in Plymouth Meeting. And with the omicron variant causing historic case surges, it’s important for ordinary Americans to have access to high-quality masks, he said.

“There a high infectiousness, a high rate of transmission — we have to go from protecting others, if we’re asymptomatic, to protecting ourselves. With omicron, it became obvious that vaccination is not necessarily going to prevent you from getting the disease. It’s preventing you from getting severely sick,” he said. “That’s probably where the thought is coming from — we can ratchet up personal protection by wearing more protective masks.”

Why are N95 masks more effective than surgical or cloth masks?

NIOSH quality-control standards require N95 masks to filter out 95% of particles larger than 0.3 microns. Kumar noted that the coronavirus itself is even smaller — 0.1 microns — but attaches to water droplets to float in the air, which are then blocked by the masks.

N95s typically have five layers, with a fine mesh filter in the middle layer, Schabacker said. The fit of the mask is important for protection, he said: “Consumers should be looking for an N95 that closely fits to your face, with a metal band and foam band on the nose, and head loops instead of ear loops. When you breathe through the mask rapidly it should collapse on you, to indicate you have a tight fit and you are protected to a higher degree,” he said.

Surgical and cloth masks are effective at protecting others — more so than the wearer, Schabacker said. Because they’re not sealed on the sides, they don’t filter as many particles as the mask wearer inhales. But they do trap the virus particles that the mask wearer might exhale.

The benefits of wearing a high-filter mask are significant, Kumar said. “We used to think it didn’t matter. But with more transmissible variants, even small amounts of the virus can infect you. So we want to block as much from entering the nose and mouth as possible,” Kumar said.

How often can an N95 mask be re-worn?

“It depends on how you use it,” Kumar said. “For people who are outside of health-care settings, about five times, or 40 hours, is what some experts are citing. However, our approach is to make sure that the mask you are using fits well, has maintained its integrity, and has a good seal. If it doesn’t meet these criteria and if it isn’t comfortable, or you can’t keep it on, you may not get all the protection of the mask.”

Schabacker said that ECRI tested the reusability of N95s in the first wave of the pandemic, when supplies were short, and concluded the masks are effective “as long as you can breathe relatively easily through it.”

“Once it starts to get moist and becomes really heavy, you have to probably change it,” he said. If an N95 mask isn’t visibly contaminated with blood, mucus, or dirt, he said, you can dry a moist mask by hanging it up in an airy place in your house. Or, if it’s not moist, put it in a paper bag, fold the mask so the inner sides aren’t coming into contact with the outside of the mask, and leave it in the bag until you need it again.

When do you need an N95 mask the most?

“Wear your N95 anytime you are indoors for extended periods of time in crowds of more than 10 people, when others may have masks off, when around mixed vaccination status — essentially whenever your risk level is increased,” Kumar said.

But risk levels won’t be the same for everyone.

“For example, if I am an immunocompromised person, I may only be going to the grocery store. This would be my riskiest activity so I would use my best mask there. But for someone with no health conditions who engages in a number of activities, this may be a different place altogether such as a basketball game,” Kumar said.

In tight settings, like public transportation, “N95 is the way to go,” Shabacker said. Shopping outdoors or in a large store might be less risky for some people, he said. “It’s relatively unlikely you’ll get a high enough dose to be infected, so I’d be more comfortable wearing a surgical mask, or double-masking with a surgical mask and a cloth mask.”

Shabacker said that in 2020, ECRI tested a number of KN95 masks — the Chinese version of N95 masks, which aren’t certified by NIOSH — and said the public should be more cautious buying those masks, as 60 to 70% of the masks ECRI tested did not filter 95% of aerosol particulates. Still, he said, KN95s are “most certainly better than surgical masks, and surgical masks are definitely better than cloth masks.”