It's a simple device that can save lives and keep people out of emergency rooms.
But masks are once again a flashpoint after the Centers for Disease Control and Prevention (CDC) recommended this week that everyone in areas with substantial or high levels of transmission, regardless of their vaccination status, return to wearing a mask in public, indoor settings and in schools, amid a concerning rise in the delta variant.
Despite a rise in cases and hospitalizations, several states are pushing back against the CDC's new guidelines -- which have changed dramatically over the past few weeks. Some governors have balked at what they've criticized as a whiplash reversion to overly draconian measures, vowing no mask mandate would succeed in their state.
The CDC's reversal comes just two months after it announced it would no longer recommend masking for vaccinated Americans, and just as the nation was breathing a collective sigh of relief at the precipitous fall of cases and hospitalizations due to the rollout of mass vaccinations.
Here are some of the states battling back against the changing guidance, and why.
No 'one size fits all'
"The time for government mask mandates is over," Texas Gov. Greg Abbott tweeted after the CDC's announcement on Tuesday, adding that "now is the time for personal responsibility."
Texas' COVID-19 cases and hospitalizations have seen a dramatic rise, with daily case averages roughly doubling in recent weeks. COVID-19 deaths in the state are also ticking up.
On Thursday, Abbott criticized President Joe Biden for the length of time it's taking the Food and Drug Administration to upgrade the vaccines to a permanent authorization from their current emergency authorization -- a concern often cited by those who are hesitant to get the shot.
For states like Texas and Iowa that have either passed laws or issued executive orders banning mask mandates, the latest CDC guidance is "counterproductive to vaccination efforts," said Iowa Gov. Kim Reynolds.
Reynolds called the CDC's recommendation "not grounded in reality or common sense," and praised herself for leading one of several states that have passed laws restricting mask mandates
"I'm concerned that this new guidance will be used as a vehicle to mandate masks in states and schools across the country, something I do not support," Reynolds tweeted.
In Arizona, another state where mask mandates are banned by law, Gov. Doug Ducey used the CDC's recommendations to criticize Biden, saying that the new mask guidance is an example of the Biden administration's "inability to effectively control the COVID-19 pandemic."
Alabama officials also said they would not be following the CDC's updated guidance. A spokesperson for Gov. Kay Ivey said the current circumstances do not warrant a "blanket one-size-fits-all" approach.
"The state of emergency has ended, and Alabama is moving forward," the spokesperson told ABC News.
'The vaccine works'
Following the CDC's announcement this week, Biden said the decision was not a relapse but "another step on our journey to defeating the virus."
"Unlike 2020, we have both the scientific knowledge and the tools to prevent the spread of this disease," Biden said. "We are not going back to that."
But some states' leaders are pointing to the vaccines' efficacy as a reason not to re-enforce masking.
"The vaccine works," said Gov. Henry McMaster of South Carolina, where a state law prohibits school administrators from requiring students to wear a mask.
Health officials stress that while the vaccines are indeed safe and effective, many states still have a substantial number of residents who are unvaccinated -- and with the exponential spread of the highly transmissible delta variant, a mask is meant to protect both wearer and bystander.
In Maryland, a health department spokesperson told ABC News that the state isn't affected by the new CDC guidance because it's not among the areas showing "high or substantial community transmission." The spokesperson said that Maryland is one of the most vaccinated states in the country, and that "blunts the impact of the delta variant."
For health experts like University of Washington professor of global health Ali Mokdad, who believes the CDC was late in reversing its guidance, the political debate over masks is "hurting our ability to contain COVID-19."
"I do not understand how masks and vaccines could be a political statement," Mokdad said. "Look at the new admissions in Florida for COVID-19 confirmed patients -- if this will not make governors pause and take this virus seriously, what will?"
Some states, like California, New Mexico and New Jersey, have welcomed the latest mask guidance.
"It's clear that the nation is at a critical moment in this COVID crisis," said Illinois Gov. J.B. Pritzker, lauding the CDC for "a hard look at where we are."
"Illinois will follow this guidance, as we always have," he said.
Left vs. right
Like other coronavirus issues, the updated mask guidance has divided parts of the country along largely political lines -- even within states.
The attorney general of Missouri, where coronavirus cases and hospitalizations continue to rage, has announced that the state government is suing St. Louis city and county for bringing back mask mandates. But that didn't stop Kansas City, on the other side of the state, from announcing Wednesday that it was also reinstating an indoor mask mandate.
Missouri Gov. Mike Parson, a Republican, called the new CDC guidance "disappointing" and "concerning" Wednesday, adding that "it only serves to disrupt" the state's slow uptick in vaccination.
In Atlanta, Mayor Keisha Lance Bottoms, a Democrat, on Wednesday issued an executive order requiring masks in public indoor spaces -- despite Gov. Brian Kemp's longstanding opposition to any mask mandate.
"We don't need mandates," Kemp, a Republican, told ABC affiliate WSB-TV this week. "We need to continue to share the data and the facts."
Georgia's cases and hospitalizations are both at more than 10% and rising.
In Florida, a spokesperson for Gov. Ron DeSantis, a Republican, told ABC News that imposing mask mandates would discourage people from getting vaccinated.
But Miami-Dade, the state's most populous county, is pushing back against the governor's ban on masks after reporting 11,000 new coronavirus infections in one day.
"When the health care system is overwhelmed, that is extremely dangerous for all of us, so we must do our part to keep people out of the hospital," Miami-Dade Mayor Daniella Levine Cava. a Democrat, said Wednesday.
Dr. Rich Besser, former acting CDC director and president of the Robert Wood Johnson Foundation, told ABC News that the pandemic is far from over and that "we do need to do more."
"We're in a very fluid situation," Besser said. "You know, there are many who wanted to declare victory over this pandemic several months ago, but it's far from over."
"We will see the end of this pandemic," said Besser, who supports a "layered approach" out of the crisis. "But until that time, we are all at risk."
ABC News' Dr. Alexis E. Carrington, Jianna Cousin and Sam Tiffany contributed to this report.