If no one else is wearing a mask, should you?

Once Hawaii drops its mask mandate later this week, no state in the United States will require everyone to wear a mask indoors to prevent the spread of COVID-19. Yet in many supermarkets, office buildings, movie theaters, and other indoor locations, some people are still masking up. But if only half, or a few, or nobody else is doing so, does the mask offer the wearer sufficient protection?

The question is becoming more urgent because even though rates of COVID-19 in most of the U.S. are currently low, they are rising in Europe—due to the fast-spreading variant Omicron BA.2—which has often presaged a spike here.

“It’s true that masks are most effective when everyone around you is wearing them. If someone is infected with COVID-19 and doesn’t know it, their mask is like putting a thumb over the end of a hose, preventing the virus from spewing,” says Jaimie Meyer, an infectious disease physician at Yale Medicine.

But she emphasizes that even when that infected person is maskless, anyone around them who has their own mask reduces the chance that those droplets will find their way to their respiratory system and sicken them.

Here’s what Meyer and other experts say about masking and how to gauge when it’s safe to ditch the mask, and when it’s not.

COVID-19 transmission in your community

In February, the U.S. Centers for Disease Control and Prevention (CDC) changed its policy on indoor masking, recommending it for healthy people in indoor settings only in communities where COVID-19 cases and hospitalizations are high.

To help figure out where masks are necessary the CDC published a new color-coded map revealing zones of low, medium, and high transmission. Areas of low risk, where people do not need to mask indoors, are indicated in green; as of March 24, this applies to most of the country.

Along with hospitalization and ICU numbers, counties are labeled red when new cases reach 200 per 100,000 residents. Several counties, especially in Montana, Kentucky, and Maine, are currently this color.

People in locations labeled yellow who are at high risk for severe illness are instructed to ask their healthcare providers whether masking is necessary. These locations also have more than 200 new cases per 100,000 but with fewer hospitalizations and ICU patients.

The recommendations are intended to provide protection on a population level and to keep healthcare systems from inundation. They are not designed to keep any individual from getting sick, says Jill Weatherhead, an infectious disease doctor at Baylor College of Medicine.

The 200-case threshold is “a really high transmission rate,” says Katelyn Jetelina, an epidemiologist at the University of Texas Health Science Center who blogs as “Your Local Epidemiologist.” To feel comfortable going without a mask, she prefers using a lower threshold, on the order of 50 cases per 100,000. Jetelina, who is vaccinated and boosted, recently shed her mask when rates in her county of Dallas fell below that number.

Rates for each county can be found on the CDC’s website.

Deciding whether to ditch your mask

Of course, masks are still mandatory for people in certain situations. When California dropped its statewide mandate, for example, it kept masking requirements in healthcare facilities, prisons, and other congregate settings. Some private business and schools also insist on masks on their premises. And the federal government continues to require them for commercial flights and other transportation.

For people in a setting where masks are optional, the calculation for whether to wear one largely depends on individual circumstances and how much you don’t want to get sick, in addition to transmission rates around you, experts say. “A lot of people have resigned themselves that they’re going to get COVID-19, but it isn’t inevitable,” Meyer says.

The strongest protection against the disease remains vaccination, Meyer stresses. According to a study published in early March in the New England Journal of Medicine, the Pfizer-BionTech shots were 85 percent effective at preventing hospitalizations and deaths in the residents of North Carolina up to seven months after their two-vaccination series. (Study participants had not received a booster, which would provide additional protection.) But masking may be the next most important thing you can do, she says.

People who have underlying health conditions or who live or work around such people must make a different mask calculation than others, Jetelina says. Those who are immunocompromised should nearly always wear a mask around others indoors, while people with a disease like diabetes that puts them at higher risk for COVID-19 complications might consider using a lower threshold, perhaps 10 cases per 100,000 in their community, she says.

Still others choose to mask because they have children who are vulnerable because they are too young to be vaccinated. Weatherhead continues to wear masks in stores and crowded indoor facilities in large part to protect her 4-year-old son.

To be effective, the CDC emphasizes masks must be worn consistently. Some people in areas with high transmission may think they are safe without a mask indoors when they remain more than six feet from others in the room. But it’s a misconception that keeping your distance inside reduces your risk of exposure completely, says Linsey Marr, professor of engineering at Virginia Tech and an expert on viral transmission. It’s true that viral particles are concentrated closest to an infected individual, she says, but just as cigarette smoke eventually spreads throughout a room, so, too, does the coronavirus.

Of course, everyone has a different level of tolerance and that should be respected, Weatherhead says. “A lot of factors are involved, and everyone’s decisions will be different,” she says.

For some people, including Meyer, “it’s exhausting to have to keep making a risk calculation depending on the situation,” which is why she has decided to keep hers on in shops and grocery stores and indoor spaces like her childrens’ basketball games, regardless of what those around her are doing. “It’s easier for me to just put on the mask and not have to decide every time,” she says.

One group who should always be masked: patients with COVID-19 who have isolated for the CDC’s recommended five-day period. During the subsequent five days, the agency instructs, assuming they are asymptomatic or their symptoms are resolving, they no longer need to isolate but must wear a mask indoors around others to reduce the chances of spreading the virus.

Mask quality and fit are key

A study from the CDC published last month in Morbidity and Mortality Weekly documents the protection that various masks provide. People routinely wearing an N95 or KN95 mask lowered their odds of testing positive by 83 percent compared with their unmasked counterparts. For surgical mask wearers, disease was reduced 66 percent and for cloth protections, 56 percent.

What this study and others like it did not specifically track is how many people around each mask-wearer were also covering their faces. But since it was conducted when California mask mandates were in place, many people were likely wearing them, observes Marr, who was not involved with MMWR study. She suspects the masks would have been somewhat less protective if more had been barefaced, but that the contrast between wearers and non-wearers would likely still be striking.

The MMWR research underscores the value of using a high quality, respirator-type mask like an N95 or KN95 versus a simple piece of cloth. In fact, the CDC, now notes that “properly fitting respirators provide the highest level of protection.”

“If there is virus in the air, your N95 is going to block over 95 percent of it,” a very high number, Marr says.

Don’t toss that mask

Anyone not currently wearing a mask still should keep it at the ready, experts say.

“I want to be optimistic because spring is here. But it seems like it might be an ominous time” because of the rise in cases in Europe fueled by Omicron BA.2, Yale’s Meyer says. She advises anyone not currently masking to pay close attention to COVID-19 rates in their area, in the event cases begin a steady uptick.

No one knows if a spike will soon materialize in the U.S., because the variant BA.2 generally doesn’t reinfect people who contracted the prior version of Omicron, according to a Danish study published last month, which has not yet been reviewed by experts. “It’s complicated to predict future spread here because it depends on how much BA.1 spread and how much more ‘wood’ the fire has left to burn,” the University of Texas’s Jetelina says.

“You should keep your mask at the ready because of what’s happening today, but also for what might happen tomorrow,” she says. “The mask helps you stay ahead of this disease.”