U.S. COVID cases are once again at a high plateau, climbing to heights not seen since late last winter.

With all eyes on the new, highly mutated COVID variant “Pirola” BA.2.86 and respiratory virus season on its way, is it time to start masking again?

Though not always en vogue politically or much fun, it was never not time to mask, many experts contend—not since COVID began circulating widely in 2020, anyway. And while masking might not be necessary in all situations (think: outdoors), it can certainly still behoove you—especially in some circumstances.

“Masking remains an effective tool to reduce your risk” of catching COVID, Dr. Georges Benjamin, executive director of the American Public Health Association, tells Fortune.

“People who are at high risk, are planning to be indoors in crowds, or who are around people whose health conditions put them at risk would benefit most from mask-wearing during this period of COVID uptick.”

Those at high risk of severe outcomes from COVID “should always consider masking in crowded indoor settings,” Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, tells Fortune.

“People should also be vigilant if they have symptoms consistent with COVID if they are planning to be in the presence of those at higher risk for severe disease,” he says, adding that such advice applies “all the time, not just now.”

To mask or not to mask? What the experts say

Dr. Stuart Ray agrees with Benjamin. He’s vice chair of medicine for data integrity and analytics at Johns Hopkins’ Department of Medicine.

When it comes to masking, there are multiple factors to consider, he says, including:

• Community transmission: How prevalent is COVID in your area? Check with your local and/or state public health department. If local levels are moderate or high, masking may be a good idea.

• Your immunity: Antibody immunity to COVID, which can prevent infection, tends to wane after three to six months. The trouble is, immunity is never bulletproof. Not all COVID strains confer the same degree of protection against all other circulating variants. And there’s no guarantee that up-and-coming variants will play by the rules we’re used to. If you’ve not been boosted or infected in the last few months, you may want to mask up.

• Your schedule: Do you have big events coming up, like a presentation that you can’t afford to be sick for? Are you planning to attend large events, like a wedding, conference, or concert? Do you intend to visit crowded places, like a mall, movie theater, or airport? Are you planning to meet with high-risk family members? If so, you might want to mask ahead of such events and/or during them—for your protection, and/or for the protection of others.

• Your risk level: Are there factors—like diabetes, obesity, advanced age, or immune status—that put you at higher risk of hospitalization or death from COVID? If so, you’ll likely want to “err” on the side of caution and mask up.

“For me, wearing a mask on mass transit and in very crowded spaces is easy and wise,” Ray says.

Another place where it makes a lot of sense to mask up: hospitals. Masking mandates in medical settings should have never been dropped, Ryan Gregory, a biology professor at the University of Guelph in Ontario, tells Fortune. He’s been assigning “street names” to high-flying variants since the WHO stopped assigning new Greek letters to them.

More broadly, he recommends respirators, air filtration devices, good ventilation, and avoiding large crowds—all mitigation measures that work regardless of the variant(s) you’re encountering and any weird new curveballs the virus throws our way.

‘Learning to live’ with the virus—wisely

For years, public health officials have said society would need to “learn to live” with COVID. But doing so should have included guidelines on when to mask, based on levels of community transmission, Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., and a top COVID-variant tracker, tells Fortune.

“We don’t have proactive non-pharmacological approaches,” Rajnarayanan says. “We’re always reactive.”

Unfortunately, the U.S. Centers for Disease Control and Prevention no longer offers a map illustrating levels of community spread. (The map was inaccurate for a while anyway, reflecting hospital bed availability in an area instead of viral activity.) And while the agency does offer a map that shows the percent of COVID tests returning positive by U.S. region, those numbers are likely to be skewed by near all-time low levels of testing. (Read: Things may appear worse than they actually are.)

Still, as of Tuesday, that map showed seven of 10 U.S. regions with a percent positivity rate of 10% to 14.9%, a category shaded yellow. The U.S. south-central region, including Texas, was worse off, with a 15% to 19.% percent test positivity rate, shaded orange. Two regions in the U.S. Northeast had more acceptable levels of percent positivity, from 5% to 9.9% and shaded green. For context, the World Health Organization initially recommended a test positivity rate of 5% or lower for communities wishing to reopen after the first lockdowns of 2020.

People should still mask indoors, Rajnarayanan says—especially in hospitals, at airports, and on planes and other modes of mass transit.

A recent study found that immunity from prior infection, vaccination, or both (known as “hybrid” immunity) was effective in preventing COVID when subjects were exposed to low or moderate doses of the virus—but not when they were intensely exposed (in this case, prisoners who lived with cellmates who had COVID, resulting in constant exposure). The findings highlight the utility of masking, even for the vaccinated, Gregory points out.

“It’s important to reduce the amount of virus inhaled,” he says. While masks should ideally be snug-fitting and high quality, “even imperfect masking would be worthwhile.”

The threat of long COVID

Personal decisions on whether or not to mask should take into account the continuing threat of long COVID, experts say. Contrary to popular belief, it’s still possible to develop the condition—even if you didn’t the first time you got COVID. What’s more, it’s possible to develop long COVID after a mild case of the virus—not just with severe cases.

A few facts to keep in mind about the post-viral illness, according to recent research:

• Long COVID can linger for at least two years, a study published this month in Nature Medicine confirmed.

• For those hospitalized during their COVID illness, the risk of death and hospitalization remains “significantly elevated” for two years, according to the study.

• For those who weren’t hospitalized during their COVID illness, the risk of death after COVID remained statistically significant for six months, researchers found. The risk of hospitalization remained elevated for about a year and a half.

• Long COVID can be more fatiguing than some late-stage cancers, according to a study published in June in BMJ Open.

• Functional impairment among long COVID patients is worse than that experienced by those who’ve had a stroke, and is similar to that experienced by patients with Parkinson’s disease, the study found.

• What’s more, quality of life was generally better in stage 4 lung cancer patients than in long COVID patients, researchers found.

Does solo-masking help?

Some experts point out that masking was always meant to be a group intervention, not a single-person one. Still, one-way masking “substantially reduces risk” of contracting COVID, Ray says, regardless of what others are doing—as long as your mask is high quality, like an N-95that it fits snugly. (Surgical masks with gaps that let air in from the sides are not, and were never, ideal.)

Another tip from Ray: Keep your cool, even if you’re surrounded by those whose opinions on masking differ. “Clashing with others who don’t wish to mask doesn’t tend to reduce risk,” he advises. Aside from the fact that people are rarely won over by arguments, such a situation could “prolong or intensify exposures, if tempers run high.” A yelling match could actually lead to greater volumes of the virus being expelled, if those yelling have COVID.