They really do work, evidence shows, and N95s are about 10 times as good as surgical ones.
Masks do prevent respiratory illness transmission and some do it better than others, a re-analysis of previously controversial data and interpretation has found.
“The policy implications of masks are most relevant for potential pandemic pathogens such as influenza or novel coronaviruses, but data on other respiratory viruses transmitted through respiratory aerosols are informative, regardless of the severity of the infection and varying degrees of airborne transmission,” the authors say.
Mask mandates were divisive during the covid pandemic, and the evidence for them was contested. A new review has sought to incorporate evidence from a variety of trial designs and disciplines to provide a clearer understanding of the benefits, drawbacks and applications of masks in the current landscape.
In short, limited time indoors, ventilation, and wearing respirators work best, especially in “pathogen-rich spaces” such as medical centres, the authors say.
Respirators are the masks that fit snugly around the mouth and nose so that all air has to go through, not around them. They protect against small particles, as well as large ones.
Viral load is higher in small aerosols shed from deep in the lungs, as covid is. These remain airborne for longer than large droplets from the upper respiratory tract.
“[T]he risk of airborne transmission increases incrementally with the amount of time the lung lining is exposed to pathogen-laden air, in other words, with time spent indoors inhaling contaminated air,” the authors say.
This spread does not require sneezing or coughing to occur. It just involves breathing in the same air.
“While fit testing and training are important and legally mandated for occupational health, some studies have shown similar levels of performance in non-fit-tested respirators used by untrained individuals, and this arrangement still outperforms other, uncertified types of face coverings,” the researchers say.
Certified N-95 respirators are between eight and 12 times better than surgical masks at filtering out aerosols, the review says. They also help prevent the wearer from spreading their infection to others.
In healthcare settings, risk of influenza-like illness was 20% lower with respirator use, either continuous or intermittent, than with surgical masks. Continuous use resulted in a 52% lower risk of infection with a clinical respiratory illness than with surgical masks.
Surgical mask use in the community was associated with an 11% lower relative risk of influenza-like or covid-like infections than no masks. There was a 37% lower risk of PCR-confirmed influenza with surgical masks plus hand hygiene measures compared with no mask use.
“Hand hygiene may protect against direct contact transmission and transmission through contaminated masks. Pathogens may be present on the outer surface of masks, resulting in self-contamination,” the authors suggest.
The review also looks at adverse effects of mask wearing. These included local irritation of skin and eyes, pressure effects, and acne from contact dermatitis. Some experience headaches and others overheating. The authors say better mask design is required, but in the meantime, adverse effects can be mitigated with topical treatment, cushioning tapes and repositioning straps away from ears, as well as regular “air breaks”.
Concerns about a risk of cardiac dysrhythmia were not borne out. A research letter stating that masks increased carbon dioxide inhalation in children was retracted soon after publication.
“Consistent findings across what is now a large body of research have shown a reassuring absence of clinically meaningful serious harms. Furthermore, no serious safety incidents have been documented despite periods of high community uptake of masking during pandemic waves,” the authors write.
However, specific groups of people experienced adverse effects that need to be weighed against the benefits of mask wearing for them, the authors said. It was not recommended in children under the age of two, however older children reported largely positive experiences of mask wearing.
For instance, in a Canadian survey of over 40,000 teenagers, 82% supported wearing masks in indoor public spaces. In other research, children reported barriers to communication and socialising. And they were concerned about comfort, fit, style and environmental factors.
A number of medical conditions ― allergic rhinitis, Alzheimer’s disease, chronic lung disease, end-stage kidney disease, epilepsy, facial conditions, heart failure, laryngeal or tracheal surgery, mental health conditions (e.g., anxiety, autism, depression, and claustrophobia), and pregnancy-related conditions ― were researched with regard to the adverse effects of mask wearing.
Alzheimer’s disease precludes it altogether. Some conditions that make mask wearing harder also increase vulnerability to disease, “underscoring the point that the risks of masking should be balanced against the benefits”, the authors write.
Mask wearing affects communication, and this has a significant impact on deaf people and others who need to see full faces to communicate. It can also have a negative impact for people who are neurodiverse, those who have cognitive difficulties, and those with trauma.
“The above impacts are best considered on a case-by-case basis and must be balanced against infection risk and vulnerability of wearers,” the authors say.
“Even if communication is more difficult, it may not be in a person’s best interests for people interacting with them to be unmasked. Instead, better communication strategies and other approaches to support ongoing masking may be more appropriate.”
Importantly, the review also considers why people choose to wear, or not to wear masks, which is influenced by diverse socio-economic, psychological, political and philosophical factors, noting that “[a]nti-mask sentiment is increasing, along with anti-vaccine sentiment”.
It also looks at ways to address associated problems not directly related to infection control, such as the two megatonnes of waste generated by disposable masks each year.
The paper, authored by high-profile researchers who themselves are often targeted for their views on infection control, delves into where the discussion around masks got so complicated – everything from conflicting ideas about knowledge and evidence, to misunderstandings and inconsistent terminology across disciplines.
Studies did not measure the same things in the same settings. They varied in quality and methodology. There were agendas, there was misinformation, there was plenty of good research as well as bad or incomplete research that was published and withdrawn but continued to be circulated. There was social media, culture, politics, psychology and sociology.
“This review was commissioned partly because of controversy around a Cochrane review which was interpreted by some people as providing definitive evidence that masks don’t work,” the authors say.
“[T]he claim that masks don’t work is demonstrably incorrect … The time is well overdue for international policy bodies to acknowledge the totality of evidence on the science of masks and masking and to show leadership in providing such messaging to policymakers, clinicians, and the public.”
