It may be safer for school kids to stay maskless in classrooms

This fall, schools will be open across the US. The few places still reluctant are being over-fearful. As noted this week in Nature, there is mounting evidence that even in the absence of vaccination for the young, neither schools nor schoolchildren are significant sources of the covid virus’s spread. On Friday, the US Centers for Disease Control issued new guidance meant to encourage reopenings by giving schools more flexibility on classroom safety. So the question isn’t whether schools should open. It’s what mitigation measures they should take when they do.

The flashpoint is masks. Some districts require them, some don’t. CDC guidelines continue to recommend them for unvaccinated students and staff. Evidence suggests that indoors, particularly when ventilation is poor, masks help prevent viral spread. Critics respond that masks are harming children. I needn’t drive far from my Connecticut home to see lawn signs calling on the state governor to “Unmask Our Kids”.

Into this maelstrom comes a research letter published in the Journal of the American Medical Association. The authors warn that we’ve spent so much time thinking about the harm done by covid that we’ve done little to assess the harm that masks can do—to children. The particular harm they have in mind is breathing air full of carbon dioxide.

At one time, the argument for masks was mainly that they kept the wearer from infecting others, but now evidence of their protective benefits is plentiful. A literature review published last year in The Lancet found that wearing either surgical masks or similar cloth masks reduced exposure by around two-thirds. Even researchers who are sceptical of the benefits concede that masks seem to offer some degree of protection in settings that involve close contact. What the JAMA letter argues is that in considering whether to mask schoolchildren, it’s necessary to spend more time balancing those benefits against the risks.

The authors, six European researchers, measured CO2 levels in the air inhaled and exhaled by 45 children with a mean age of 10.7. They took readings without face masks, then with face masks of two different types: surgical masks and filtration masks. The masks were randomized and blinded. The CO2 content of the ambient air in the laboratory was kept at or below 0.1%—that is, 1,000 ppm. Past studies suggest that when the carbon dioxide level in classroom air is above this level, both respiratory illness and absenteeism increase.

The results are worrisome. After just three minutes of mask wearing, the mean CO2 levels for inhaled air were between 13,120 and 13,910 ppm. That’s not a typographical error. The carbon dioxide content of the air inside the masks—the air being inhaled—was about 13 times what previous research suggests is safe. And there’s this: “The youngest children had the highest values, with one 7-year-old child’s carbon dioxide level measured at 25,000 ppm.”

Those figures are for three minutes. If the average school day is six hours long, the children would be masked for close to 360 minutes. With time off for eating and outdoor exercise, perhaps it’s better to say 300 minutes . And the research has implications well beyond the classroom, as parents everywhere struggle to decide when to mask their children and for how long.

It’s odd that the issue has had so little public discussion. Studies published earlier in the pandemic already pointed to potentially higher CO2 levels among health-care workers who wore protective equipment for long periods of time. Why? Because the workers are re-breathing the same CO2 they’ve previously exhaled. The masks seem to be trapping what the lungs are trying to get rid of. Given that other studies have found similar problems in adults, we should surely be spending more time studying the effect on children.

That’s not to say we should accept uncritically the conclusions of the JAMA letter. As the authors admit, with refreshing candour, the study has its limitations. The sample size is small. Moreover, the experiment was performed in a laboratory; it’s not a study of similar cohorts in the real world. And at least a part of the CO2 buildup might be attributable to the nervousness of children who knew themselves to be experimental subjects. So before drawing dramatic conclusions, one wants to learn whether the numbers replicate.

By the same token, mask supporters shouldn’t pounce on these limitations as a reason to ignore the study. A blithe dismissal would only contribute to our tragic inability to engage in serious debate on serious issues. And since we all share the goal of doing what’s best for our children, we must get this right. With US schools reopening, we need to delve far more deeply before we can say with assurance whether the benefits of masks in the classroom indeed outweigh the risks.

Stephen L. Carter is a Bloomberg Opinion columnist and a professor of law at Yale University