To mask or not to mask? We now have an answer to that question

A comprehensive new review published in Clinical Microbiology Reviews provides strong evidence that masks and respirators are effective in reducing the transmission of respiratory infections like COVID-19. The review, conducted by an international team of 13 researchers, analyzed over 400 studies from multiple disciplines, including epidemiology, public health, engineering, and social sciences.

"Our review confirms that masks work, with a clear dose-response effect," says lead author Professor Trisha Greenhalgh from the Nuffield Department of Primary Care Health Sciences, University of Oxford. 

"The more consistently and correctly you wear a mask, the better protected you are. Respirators, when worn continuously, provide even greater protection than ordinary masks."

Masks, including cloth face coverings and disposable medical masks, help reduce the spread of respiratory droplets and aerosols. Respirators, such as N95 and FFP2 devices, are designed to filter out smaller airborne particles and fit more tightly to the face, providing a higher level of protection.

"In a world of misinformation, questioning the effectiveness of everything from masking to vaccines, it's important to have solid science to support any assertion," says Dr. Joe Vipond, MD, co-author and clinical assistant professor at UCalgary's Cumming School of Medicine. 

"This is the definitive answer on masks, looking beyond the narrow view of randomized controlled trials to the entirety of the evidence. And behold, the current science upholds the standards and protocols that for decades have protected health care workers, and more recently the public, from biohazards. 

"At a time of ongoing outbreaks in our hospitals, and a threatening H5N1 epidemic, it is essential that health-care leaders, and politicians, understand the utility and role that masks play in protecting patients and workers."

Co-author Matt Oliver, PEng, says, “Respiratory protection using filtering respirators is a real-world use case that is well-suited to analysis using quantitative engineering and occupational hygiene methods. 

"Much like aircraft or bridge design, respirators are constructed to standards which represent the challenges and situations of use in a variety of field settings. Since we understand physics, the performance of respirator designs can be modelled with very high fidelity."

The team's novel contributions include re-analyses of key clinical trials and observational studies, as well as a synthesis of evidence from fields ranging from fluid dynamics to anthropology. This comprehensive approach allowed the researchers to not only assess the effectiveness of masks under experimental conditions, but also to explore the real-world factors that influence their use and impact.

Dr. Mark Ungrin, PhD, associate professor in the University of Calgary’s Faculty of Veterinary Medicine and head of the Ungrin lab says, "Science integrates all available information — there is no one magic method that erases or overrides other kinds of evidence. The idea of clinical trials as a single 'gold standard' can be useful in the right context, where you don’t have the time, resources and/or subject-matter expertise necessary to pull together all the relevant knowledge. But it’s important to remember that’s a shortcut, not a thorough scientific approach. 

"This is particularly true for questions like the protection respirators that provide against aerosol hazards, which have decades of both laboratory and workplace evidence showing they are effective, and where a rigorous trial is often impractical. 

"A given trial may show that a specific set of instructions for using respirators is not well designed, for example, but doesn’t necessarily say much outside that context — making the kind of integration across disciplines our transdisciplinary team has been working on essential for a deeper understanding."

Drawing parallels from the effective use of respirators, a certain depth of understanding can only be achieved through a transdisciplinary approach. Similarly, the complexity of issues such as drinking during pregnancy calls for a comprehensive evaluation of interdisciplinary evidence rather than relying solely on randomized controlled trials.

While the review found no serious harms from mask-wearing, it did identify some challenges, such as discomfort, communication difficulties — for hearing-impaired people, for example — and environmental waste. However, the authors frame these as opportunities for further research and improvement rather than fundamental flaws.

"We need to see these challenges as a call to action," says co-author Dr. Amanda Kvalsvig, an epidemiologist based at the University of Otago, who is herself deaf. "By investing in better design, more inclusive policies, and clearer communication, we can optimize masks for real-world use and ensure that everyone can benefit from this powerful public health tool."

The review also highlights the importance of clear, consistent public health messaging to support mask use and combat misinformation. While mask mandates can be effective, the authors emphasize the need for context-specific assessments that consider cultural factors and public acceptability.

"Masks are not just a technical intervention, but also a social and cultural one," says co-author Professor Deborah Lupton from the University of New South Wales. "To be effective, mask policies need to be grounded in an understanding of people's beliefs, behaviours, and real-world constraints."

Looking forward, the researchers call for further studies to improve and optimize mask design, explore new technologies like nanotechnology, and develop more sustainable and inclusive solutions. They also emphasise the need for ongoing public engagement to bring about more evidence-based and constructive conversations around masks.

"This review shows that masks are a valuable tool in our pandemic response toolkit," says Greenhalgh. "By continuing to build the evidence base, innovate in design, and engage the public, we can harness the full potential of masks to protect public health now and in future respiratory pandemics."