For weeks, I have been watching coronavirus cases drop across the United States. At the same time, cases were heading skyward in many places in Europe, Asia and Oceania. Those surges may have peaked in some places and seem to be on a downward trajectory again, according to Our World in Data.

Much of the rise in cases has been attributed to the omicron variant’s more transmissible sibling BA.2 clawing its way to prominence. But many public health officials have pointed out that the surges coincide with relaxing of COVID-19 mitigation measures.

People around the world are shedding their masks and gathering in public. Immunity from vaccines and prior infections have helped limit deaths in wealthier countries, but the omicron siblings are very good at evading immune defenses, leading to breakthrough infections and reinfections. Even so, at the end of February, the U.S. Centers for Disease Control and Prevention posted new guidelines for masking, more than doubling the number of cases needed per 100,000 people before officials recommended a return to the face coverings (SN: 3/3/22).

Not everyone has ditched their masks. I have observed some regional trends. The majority of people I see at my grocery store and other places in my community in Maryland are still wearing masks. But on road trips to the Midwest and back, even during the height of the omicron surge, most of the faces I saw in public were bare. Meanwhile, I was wearing my N95 mask even when I was the only person doing so. I reasoned that I was protecting myself from infection as best I could. I was also protecting my loved ones and other people around me from me should I have unwittingly contracted the virus.

But I will tell you a secret. I don’t really like wearing masks. They can be hot and uncomfortable. They leave lines on my face. And sometimes masks make it hard to breathe. At the same time, I know that wearing a good quality, well-fitting mask greatly reduces the chance of testing positive for the coronavirus (SN: 2/12/21). In one study, N95 or KN95 masks reduced the chance of testing positive by 83 percent, researchers reported in the February 11 Morbidity and Mortality Weekly Report. And school districts with mask mandates had about a quarter of the number of in-school infections as districts where masks weren’t required (SN: 3/15/22).

With those data in mind, I am not ready to go barefaced. And I’m not alone. Nearly 36 percent of the 1,916 respondents to a Science News Twitter poll said that they still wear masks everywhere in public. Another 28 percent said they mask in indoor crowds, and 23 percent said they mask only where it’s mandatory. Only about 12 percent have ditched masks entirely.

Some poll respondents left comments clarifying their answers, but most people’s reasons for masking aren’t clear. Maybe they live in the parts of the country or world where transmission levels are high and hospitals are at risk of being overrun. Maybe they are parents of children too young for vaccination. Perhaps they or other loved ones are unvaccinated or have weakened immune systems that put them at risk for severe disease. Maybe, like me, they just don’t want to get sick — with anything.

Before the pandemic, I caught several colds a year and had to deal with seasonal allergies. Since I started wearing a mask, I haven’t had a single respiratory illness, though allergies still irritate my eyes and make my nose run. I’ve also got some health conditions that raise my risk of severe illness. I’m fully vaccinated and boosted, so I probably won’t die if I catch the virus that causes COVID-19, but I don’t want to test it (SN: 11/8/21). Right now, I just feel safer wearing a mask when I’m indoors in public places.

I’ve been thinking a lot about what would convince me that it was safe to go maskless. What is the number or metric that will mark the boundary of my comfort zone?

The CDC now recommends using its COVID-19 Community Levels map for determining when mask use is needed. That metric is mostly concerned with keeping hospitals and other health care systems from becoming overwhelmed. By that measure, most of the country has the green light to go maskless. I’m probably more cautious than the average person, but the levels of transmission in that metric that would trigger mask wearing — 200 or more cases per 100,000 population — seem high to me, particularly since CDC’s prior recommendations urged masking at a quarter of that level.

The metric is designed for communities, not individuals. So what numbers should I, as an individual, go by? There’s always the CDC’s COVID-19 Integrated County View that tracks case rates and test positivity rates — the percentage of tests that have a positive result. Cases in my county have been ticking up in the last few days, with 391 people having gotten COVID-19 in the last week — that’s about 37 out of every 100,000 people. That seems like relatively low odds of coming into contact with a contagious person. But those are only the cases we know about officially. There may be many more cases that were never reported as people take rapid antigen tests at home or decide not to test. There’s no way to know exactly how much COVID-19 is out there.

And the proportion of cases caused by BA.2 is on the rise, with the more infectious omicron variant accounting for about 35 percent of cases nationwide in the week ending March 19. In the mid-Atlantic states where I live, about 30 percent of cases are now caused by BA.2. But in some parts of the Northeast, that variant now causes more than half of cases. The increase is unsettling but doesn’t necessarily mean the United States will experience another wave of infections as Europe has. Or maybe we will. That uncertainty makes me uncomfortable removing my mask indoors in public right now.

Maybe in a few weeks, if there’s no new surge in infections, I’ll feel comfortable walking around in public with my nose and mouth exposed. Or maybe I’ll wait until the number of cases in my county is in single digits. I’m pretty sure there will come a day when I won’t feel the need to filter every breath, but for me, it’s not that time yet. And I truthfully can’t tell you what my magic number will be.

Here’s what I do know: Even if I do decide to have an unmasked summer, I will be strapping my mask back on if COVID-19 cases begin to rise again.

Some bacteria carry tiny syringes filled with chemicals that may thin out competitors or incapacitate predators. Now, researchers have gotten up-close views of these syringes, technically known as contractile injection systems, from a type of cyanobacteria and a marine bacterium.

Figuring out how key parts of the molecular syringes work may help scientists devise their own nanomachines. Artificial injection machines could direct antibiotics against troublesome bacteria while leaving friendly microbes untouched.

Genes encoding pieces of the injection machinery are found in many bacterial species. But, “just by looking at the genes, it’s quite hard to predict how these contractile injection systems work,” says Gregor Weiss, a cellular structural biologist at ETH Zurich.
So Weiss and colleagues examined bacterial syringes using cryo-electron microscopy, in which cells are flash frozen to capture cellular structures as they typically look in nature (SN: 6/22/17).

Previously, researchers have found syringes anchored in some bacteria’s outer membranes, where the bacteria can shoot their payload into cells they bump into. Other species’ injectors squirt their contents into the environment.

But in a type of cyanobacteria called Anabaena, the syringes are in an unusual place, nestled in the membrane of the internal structure where the bacteria carry out photosynthesis, Weiss and colleagues report in the March Nature Microbiology. Buried inside the cells, “it’s hard to imagine how [the syringes] could get out and interact with the target organism,” Weiss says.
Anabaena may use its syringes against itself to trigger programmed cell death when the cyanobacteria come under stress. In the team’s experiments, ultraviolet light or high salt levels in water triggered some syringes to dump their payload. That led to the death of some Anabaena cells in the long chains that the cyanobacteria grow in, forming hollow “ghost cells.”

Ghost cells shed their outer wall and membrane, exposing unfired syringes in the inner membrane to the outside. The ghosts may act like Trojan horses, delivering their deadly payload to predators or competitors, the team hypothesizes. The researchers haven’t yet found which organisms are the probable targets of Anabaena’s syringes.

Inside a type of marine bacteria called Algoriphagus machipongonensis, the story is a bit different. Here, the syringes have a different architecture and float unmoored within the bacterial cell, ETH Zurich’s Charles Ericson and colleagues report in the March Nature Microbiology. The injectors are also found in the liquid in which the bacteria are grown in the laboratory, but how they get out of the cell is a mystery. Perhaps they are released when the bacteria die or get eaten by a predator, Ericson says.

The team also found two proteins loaded inside the Algoriphagus’ syringes, but what those proteins do isn’t known. The researchers tried genetically engineering E. coli to produce one of the proteins, but it kills the bacteria, says study coauthor Jingwei Xu, also at ETH Zurich.
Comparing the structures of syringes from various species, the researchers identified certain structures within the machines that are similar, but slightly different from species to species. Learning how those modifications change the way the injectors work may allow researchers to load different cargoes into the tubes or target the syringes against specific bacteria or other organisms. “Now we have the general blueprint,” Ericson says, “can we re-engineer it?”

You can never have too much ice cream, but you can have too much ice in your ice cream. Adding plant-based nanocrystals to the frozen treat could help solve that problem, researchers reported March 20 at the American Chemical Society spring meeting in San Diego.

Ice cream contains tiny ice crystals that grow bigger when natural temperature fluctuations in the freezer cause them to melt and recrystallize. Stabilizers in ice cream — typically guar gum or locust bean gum — help inhibit crystal growth, but don’t completely stop it. And once ice crystals hit 50 micrometers in diameter, ice cream takes on an unpleasant, coarse, grainy texture.

Cellulose nanocrystals, or CNCs, which are derived from wood pulp, have properties similar to the gums, says Tao Wu, a food scientist at the University of Tennessee in Knoxville. They also share similarities with antifreeze proteins, produced by some animals to help them survive subzero temperatures. Antifreeze proteins work by binding to the surface of ice crystals, inhibiting growth more effectively than gums — but they are also extremely expensive. CNCs might work similarly to antifreeze proteins but at a fraction of the cost, Wu and his colleagues thought.

An experiment with a sucrose solution — a simplified ice cream proxy — and CNCs showed that after 24 hours, the ice crystals completely stopped growing. A week later, the ice crystals remained at 25 micrometers, well beneath the threshold of ice crystal crunchiness. In a similar experiment with guar gum, ice crystals grew to 50 micrometers in just three days.
“That by itself suggests that nanocrystals are a lot more potent than the gums,” says Richard Hartel, a food engineer at the University of Wisconsin–Madison, who was not involved in the research. If CNCs do function the same way as antifreeze proteins, they’re a promising alternative to current stabilizers, he says. But that still needs to be proven.

Until that happens, you continue to have a good excuse to eat your ice cream quickly: You wouldn’t want large ice crystals to form, after all.