Just when you thought masks were so 2020, more people are wearing them again as COVID hospitalizations and deaths have increased, and flu, RSV, and other illnesses also are surging in what’s being called a “tripledemic.”

Public health officials in Washington state, Los Angeles, and New York are urging people to wear masks indoors — especially in crowded areas like public transit. Earlier this month, CDC director Rochelle Walensky also recommended people wear masks again during the holiday season to prevent the spread of respiratory viruses, including COVID, flu, and RSV.

But some people are still debating the basic fact that masks work — nearly three years after the start of the pandemic. Congressman Thomas Massie of Kentucky recently tweeted that “the data shows masks don’t work.” Marjorie Taylor Greene, another actual member of Congress, also questioned unironically how masks could possibly prevent COVID if pants can’t protect from farts. (In case you’re wondering, as a University of Virginia chemistry professor explained in 2020, gaseous fart molecules are way smaller than particles containing viruses, which is why they pass through even the best-quality undies.)

We asked experts to break down the evidence — again — when it comes to masks and respiratory viruses, when and where they are wearing them now, and when it’s OK to skip them.

So do masks really work? “Yes,” said Dr. Waleed Javaid, epidemiologist and director of infection prevention and control at Mount Sinai Downtown in New York City. “As we saw during this COVID pandemic, when we had increased use of masks, we saw a decrease in all respiratory infections.”

Of course, masks have drawbacks: They can be uncomfortable and make it harder for some people to communicate. But contrary to some conspiracy theories and junk science, wearing masks isn’t physically harmful, even for kids, and they can help ensure you don’t get sick during the holidays.

Masking misinformation

Then why don’t some people believe they work? “It’s a combination of misinformation, fatigue, and ideology, coupled together with missed opportunities for public health messaging,” said Dr. Luis Ostrosky-Zeichner, chief of infectious diseases with UTHealth Houston and Memorial Hermann Hospital in Houston.

There’s so much conflicting info out there that it’s not surprising people may be confused.

During a crisis, government institutions should proactively share information and anticipate there will be some misinformation that will affect how people respond, said Julia Raifman, assistant professor of health law, policy, and management at the Boston University School of Public Health. “Unfortunately, we have not seen the CDC leadership effectively communicate information on masks and mask policies.”

Articles in the New York Times and Bloomberg on the supposed ineffectiveness of mask mandates (the latter of which was highlighted in a not-funny Saturday Night Live sketch last March) sent confusing messages about mask policies, Raifman said. In short, if you actually read the articles, which were published earlier this year, one reason mask mandates may not work as well as they should is because people are not wearing masks consistently and correctly.

It doesn’t help that people in positions of power continue to deliberately muddy the waters.

“It’s unfortunate that masking has been so politicized, and messaging like this from public figures is confusing and detrimental to public health efforts, ultimately putting vulnerable people at risk,” Ostrosky-Zeichner said.

Dodging droplets

But if you know a doubter (or are one) who’s open to actual science from people who’ve been to medical school, here’s a refresher on how masks work. Respiratory viruses like SARS-CoV-2, RSV, and the flu spread through respiratory droplets, produced during breathing, Javaid said, adding, “These droplets are blocked using masks.”

And this method works best if the person exhaling that droplet-laden breath and the person potentially at risk for inhaling it are both wearing masks. “Masks are most effective if the person with COVID and the people around them are wearing masks,” Raifman said. “This is what universal mask policies achieve.”

The effectiveness of masks isn’t new information for doctors, who have worn them for decades. (Think about it: Would you want a surgeon operating on you without one?)

“Surgical/medical masks are designed to prevent droplets from entering our respiratory system; that has been our understanding before the pandemic,” Javaid said. “[This] was proven useful during the COVID pandemic as the majority of COVID infections spread through respiratory droplets.”

Certain masks, such as N95s, which filter 95% of all particles, also protect against smaller, airborne aerosols that can contain viruses. These aerosols can hang in the air longer and evade lower-quality masks.

“The higher the quality of the mask, the higher the degree of protection offered to the wearer and those around them,” Ostrosky-Zeichner said.

The overwhelming scientific evidence points to masks’ effectiveness. Many, many, many studies (the CDC lists 90 of them through 2021) show that masks reduce transmission rates of COVID.

“There is ample scientific evidence, including both large population-based observational studies and now randomized trials, that prove that masks reduce the transmission of COVID-19 and other viral respiratory illnesses,” Ostrosky-Zeichner said. “From a scientific standpoint, this has never been controversial.”

Mask mandates do work, and there’s science to back it up

The best way to show that masks work is to look at COVID cases over time in areas with different mask policies, Raifman said. (Carefully constructed randomized control trials, the gold standard for seeing if something works, aren’t practical, safe, or even ethical during a pandemic.)

“High-quality evidence — as well as logic — indicates masks are associated with reduced transmission, and mask policies are especially effective,” she added — and the most rigorous peer-reviewed studies are consistent in showing that mask mandates are associated with reduced rates of viral transmission.

One strong example is a New England Journal of Medicine study, which was published in November. (Raifman coauthored an accompanying editorial.) Researchers had a unique opportunity to assess the effectiveness of masks when most Boston-area schools removed their mask mandates in February 2022 — except two districts.

Those two districts — even with inferior ventilation systems, without specifying the type of masks worn, or even whether they were worn correctly — reported a reduced COVID rate than the other districts that no longer required students to wear masks. The maskless districts had nearly 45 more cases per 1,000 students and staff, adding up to nearly 12,000 more cases — just under 30% of cases in all districts — over the 15-week study period.

In one of the largest trials, researchers from Yale and Stanford provided free masks to over 340,000 people in rural villages in Bangladesh. In some villages, volunteers promoted mask-wearing, so much so that 43% of people wore masks compared with 11% in villages where they were not heavily promoted. In those places where more people wore masks, there was about a 10% reduction in COVID symptoms and cases. In people over 60, the effect of wearing surgical masks was even more striking, with a 35% reduction in symptomatic COVID cases, according to the study published in January 2022 in the journal Science.

Mask critics like to point to a controversial 2020 Danish study in which about 3,000 people were randomly assigned to wear a surgical mask when outside their home and 3,000 were not. After a month, 42 of the mask-wearing people got COVID compared to 53 mask-free people, which was not a statistically significant difference.

However, critics of the study say both the research and its interpretation in the media were flawed. Despite press reports that the study was evidence masks don’t work, the authors themselves found their research to have “inconclusive results” and said the findings should not be used to conclude that community mask-wearing doesn’t work because the trial had a number of shortcomings and did not test universal masking.

Which mask should you wear?

Your personal level of protection when others aren’t masked, though, may also depend on what type of mask you’re wearing, your own personal risk (with people who are immunocompromised needing greater protection), and whether germs are at peak level of circulation. (You can check the CDC for COVID levels, RSV, and more information.)

Early in the pandemic, the public was asked to save the highest-quality masks for healthcare workers, so people donned cloth masks — or what’s known as “face doilies” to anti-maskers.

But today, an abundant supply of superior masks means we have more options to choose from.

“N95 or higher masks filter out more particles from air, even smaller than droplets, and are helpful in certain situations where there are a lot more particles in the air,” Javaid said. (KN95s also filter a high number of particles, but they’re not regulated by US standards as N95s are.) “Surgical/medical masks are good for general purpose use, easy to wear, and helpful in reducing infections from day-to-day exposures. Cloth face masks also provide some level of protection and are useful for daily use, although the protection is likely below the level of medical/surgical masks.”

No one is claiming masks are perfect, or that if you wear one you’ll definitely never catch a respiratory virus. But consider the umbrella analogy: Using one in the rain won’t totally stop you from getting wet, but it will protect you from getting soaked. And if you use one of those giant golf umbrellas (like using an N95 mask instead of cloth), you’ll be even more protected than with a tiny fold-up umbrella that fits in your purse.

So what do we do now, when mask mandates have ended, transmission is down (yet trending back up), and we have effective treatments and vaccines? Back to the umbrella analogy, you don’t need to use one when it’s not raining.

Many people — mostly those who are generally healthy — stopped wearing masks when mandates were lifted in 2022. However, it’s a good idea to mask up to enhance your personal protection in crowded, indoor places when viruses are circulating at high levels, as they are in some of the US right now. For example, you may not want you or your children to get sick with RSV or flu during a surge when hospitals are stretched to the max.

“In certain situations, I wear a mask in public, for example during commuting, in busy trains, or on airplanes,” Javaid said. “I am vaccinated against the flu, and vaccinated and boosted against COVID — I have received the bivalent [recent] booster as well — but I will still wear a mask in overcrowding situations, as there are many viruses around and I do not want to get infected.”

As Javaid points out, masking also protects against the flu and RSV, which is particularly important if you have little ones at home. RSV cases are currently surging, with pediatric units in hospitals overflowing and hourslong waits in pediatric ERs. On Nov. 14, the American Academy of Pediatrics called for an emergency declaration and response from the government. Flu cases are way up as well, with the CDC reporting the highest levels of hospitalizations from influenza that it has seen in a decade for this time of year.

“Masks do work against all common respiratory viral illnesses, including COVID-19, RSV, and influenza,” Ostrosky-Zeichner said, so you can use them to help stave off this “tripledemic.”

When to cover up

Today, universal mask recommendations may not be necessary in areas of the country with low transmission, but that doesn’t mean that there might not still be a renewed need for them if we fail to keep viral infections down.

“Everyone should wear a mask in a high-risk situation, primarily a crowded indoor space, in an area where there is more than minimal COVID transmission risk,” Ostrosky-Zeichner said. “Wearing a mask in the winter season may be the new normal, much like in some Asian countries.”

Raifman agrees that masks have their time and place and may again be widely necessary. “Ideally, we would develop rational approaches to implementing mask policies when and where they are most needed,” she said. “Examples include when there is a surge of a new variant, where we anticipate crowding and travel may contribute to a potential surge — such as on flights and transit over the holidays, and when hospitals are above capacity, as many pediatric hospitals are now.”

Debating the positives and negatives of mask mandates, though, is a somewhat different argument than challenging the clearly scientific fact of mask effectiveness. And although some media outlets seem determined to stoke fear of mask mandates, no one wants to don masks everywhere for the rest of eternity. After all, wearing masks doesn’t have to be all the time or not at all (at least for people who are generally healthy) — right now, it seems to be somewhere in between.

“My hope is that we can make the decision to wear a mask or not based on our communities and those around us as well as ourselves,” Raifman said.