Raina MacIntyre: Cloth masks should be washed appropriately everyday

In 2011, we carried out a  randomised controlled clinical trial of cloth masks in Vietnam, because in the course of doing face mask research, we had noticed that cloth masks were widely used by healthcare workers and members of the community in Asia. Yet, there was very little research evidence on the use of cloth masks. 

In many Asian countries, healthcare workers have to purchase and bring their own mask to work. Cloth masks, being re-usable, are a more cost-effective option. Until the covid-19 pandemic, the WHO guidelines and most national level guidelines did not mention cloth masks at all. There was no recognition of the widespread use of cloth masks in low income countries and an assumption that supply of disposable masks, which have long since replaced cloth masks in high income countries, would be plentiful. Who would have ever imagined that we would face a global shortage of disposable masks in 2020, and that even high-income countries would turn to cloth face coverings for health workers? 

During the covid-19 pandemic, our study was the only available published randomised controlled trial on the effectiveness of cloth masks. The findings, therefore, have been the subject of heated debate. We found that cloth masks when compared to surgical masks do not protect healthcare workers, and may even increase the risk of infection. This has been disputed by “pro-cloth mask groups” during a huge groundswell of support for community masking, and has also been used by “anti-maskers” to argue against community use of cloth masks. 

The study went from being barely noticed from the time of publication in 2015 to being one of the most highly read and contentious papers on BMJ Open during the pandemic. Health workers around the world contacted us, as they were unable to obtain medical masks or respirators, and were desperate for advice. More than one asked us “if I cannot get a medical mask, is it better to treat covid-19 patients with no mask, rather than use a cloth mask?” Our advice was that healthcare workers should not work in inadequate personal protective equipment (PPE), and that healthcare workers should not treat covid-19 patients without respiratory protection as a matter of work health and safety. Others queried the value of cloth masks in the general community, and we stated that the findings were specific for the 2-layered cotton mask used in the healthcare setting. Our findings do not preclude well designed cloth masks being protective in a community setting. A meta-analysis of observational data showed that a 12-layered cloth mask protected as well as a surgical mask during the SARS epidemic in 2003. In other research, we have shown that even a single layered cloth mask prevents respiratory emissions better than no mask, two layers is better than one, and a three-layered surgical mask is even more protective. A well-designed cloth mask can be made using a few, including multiple layers, good facial fit, optimal fabric, and a water-resistant outer layer. Washing is the other key requirement.

Unlike disposable masks which are single-use devices, cloth masks need to be reused, and must be washed in hot water and soap after daily use. The healthcare workers who took part in our 2015 trial reported washing their masks on 92% of days of follow up, with 80% doing the washing themselves. We wondered if the adequacy of washing had a role in the performance of cloth masks in the intention-to-treat analysis. It turns out this may be the case. In a post-hoc analysis, published today on BMJ Open, we found that both surgical masks and cloth masks can become contaminated with viruses after use, but only cloth masks were re-used. The healthcare workers whose cloth masks were washed in the hospital laundry were as well protected as surgical mask users. It was only the cloth masks that were washed by hand in the hospital wash basins which did not work as well. This may explain the poor performance of cloth masks in our original 2015 RCT, (because 80% hand-washed their masks) and raises several important issues.

Firstly, washing masks after every use is essential, and must be a routine part of the instructions for cloth mask use. Cloth masks, especially if made of absorbent material such as cotton, can become damp and contaminated.  Washing itself must be done in water that is at least 60 degrees Celsius with soap. Handwashing in cold or lukewarm water, which may have been the case for healthcare workers in our trial, is inadequate.  

Secondly, in the case of busy healthcare workers, as a matter of work health and safety, provision of clean masks on a daily basis is important. It is possible that healthcare workers in our trial who said they washed their masks either did so in a cursory fashion, or not at all. The additional burden of having to clean their masks for re-use may pose a risk for healthcare workers. For community members using a cloth mask, having at least two will ensure there is a clean mask available daily.

In many countries around the world, shortages of PPE have led to widespread cloth mask use. In 2020, there has been a proliferation of research on fabrics, fit, filtration and design of cloth masks, which will undoubtedly lead to more protective cloth masks and good DIY instructions. There is growing evidence that SARS-COV-2 can be spread by respiratory aerosols, so universal face mask use along with hand washing and physical distancing is important for infection control. Proper daily washing of cloth masks may also be important to ensure protection.

C Raina MacIntyre is Professor of Global Biosecurity, NHMRC Principal Research Fellow and Head of the Biosecurity Program at the Kirby Institute, UNSW. She leads a research programme in control and prevention of infectious diseases. 

Twitter: @GlobalBiosec @KirbyInstitute

Competing interests: C Raina MacIntyre received funding currently from the National Health and Medical Research Council. In the past five years she has received research grant funding from Sanofi and Seqirus.