The most rigorous and comprehensive analysis of scientific studies conducted on the efficacy of masks for reducing the spread of respiratory illnesses — including Covid-19 — was published late last month. Its conclusions, said Tom Jefferson, the Oxford epidemiologist who is its lead author, were unambiguous.

“There is just no evidence that they” — masks — “make any difference,” he told the journalist Maryanne Demasi. “Full stop.”

But, wait, hold on. What about N-95 masks, as opposed to lower-quality surgical or cloth masks?

“Makes no difference — none of it,” said Jefferson.

What about the studies that initially persuaded policymakers to impose mask mandates?

“They were convinced by nonrandomized studies, flawed observational studies.”

What about the utility of masks in conjunction with other preventive measures, such as hand hygiene, physical distancing or air filtration?

“There’s no evidence that many of these things make any difference.”

These observations don’t come from just anywhere. Jefferson and 11 colleagues conducted the study for Cochrane, a British nonprofit that is widely considered the gold standard for its reviews of health care data. The conclusions were based on 78 randomized controlled trials, six of them during the Covid pandemic, with a total of 610,872 participants in multiple countries. And they track what has been widely observed in the United States: States with mask mandates fared no better against Covid than those without.

No study — or study of studies — is ever perfect. Science is never absolutely settled. What’s more, the analysis does not prove that proper masks, properly worn, had no benefit at an individual level. People may have good personal reasons to wear masks, and they may have the discipline to wear them consistently. Their choices are their own.

But when it comes to the population-level benefits of masking, the verdict is in: Mask mandates were a bust. Those skeptics who were furiously mocked as cranks and occasionally censored as “misinformers” for opposing mandates were right. The mainstream experts and pundits who supported mandates were wrong. In a better world, it would behoove the latter group to acknowledge their error, along with its considerable physical, psychological, pedagogical and political costs.

Don’t count on it. In congressional testimony this month, Rochelle Walensky, director of the Centers for Disease Control and Prevention, called into question the Cochrane analysis’s reliance on a small number of Covid-specific randomized controlled trials and insisted that her agency’s guidance on masking in schools wouldn’t change. If she ever wonders why respect for the C.D.C. keeps falling, she could look to herself, and resign, and leave it to someone else to reorganize her agency.

That, too, probably won’t happen: We no longer live in a culture in which resignation is seen as the honorable course for public officials who fail in their jobs.

But the costs go deeper. When people say they “trust the science,” what they presumably mean is that science is rational, empirical, rigorous, receptive to new information, sensitive to competing concerns and risks. Also: humble, transparent, open to criticism, honest about what it doesn’t know, willing to admit error.

The C.D.C.’s increasingly mindless adherence to its masking guidance is none of those things. It isn’t merely undermining the trust it requires to operate as an effective public institution. It is turning itself into an unwitting accomplice to the genuine enemies of reason and science — conspiracy theorists and quack-cure peddlers — by so badly representing the values and practices that science is supposed to exemplify.

To Con’t Reading.