IF I had to write a list of the things that have caused the most harm during this pandemic, the general public being required by law to wear face coverings in indoors spaces like shops and buses wouldn’t be one of them, but the decision by the UK government to make this voluntary from Monday has been controversial.

In Scotland, face coverings will still be required for the foreseeable future and also in Wales, with the exception of pubs and restaurants. There is a separate debate about their use in secondary schools where the balance of risks and benefits is more difficult.

There are also genuine issues with mask wearing for people who are deaf or experiencing hearing loss and, of course, some people are exempt for a variety of reasons. But for most adults it does not cause harm, in comparison to other harms the pandemic has caused such as illness and death, unemployment, separation from friends and family, loss of education or training, or poor mental health.

READ MORE: Covid Scotland: 2,529 cases and four new deaths in past 24 hours

So why have we been asked to cover our nose and mouth when we visit indoor public places for the past year? Now seems the right moment to revisit what research can tell us about that, including from new studies. It’s fair to say the evidence has strengthened regarding the role they can play in reducing virus transmission.

Early on in the pandemic, the World Health Organisation was sitting on the fence about masks. So were public health agencies here and in the US. They pointed to lack of high quality studies and also possible unintended consequences like people transferring the virus to themselves by touching used masks or that people wearing them would take other risks (like avoiding distancing).

Neither of these concerns were supported by solid evidence – and in fact for the latter, subsequent surveys found that people who wore masks in public places were the same people who were more likely to follow other public health guidance. By last summer, including when it became apparent that the virus could be transmitted not just by droplets but through the air, guidance on masks changed and most countries required them as part of measures to control the pandemic.

Most studies of the effectiveness of face masks have been conducted in health care settings and focus on whether they protect the person wearing the mask from infection. There are far fewer studies on the extent to which masks protect others when the person wearing the mask might have Covid-19 but not have symptoms. This type of asymptomatic infection is common – we know this now, but we didn’t earlier in the pandemic.

So the importance of masks has grown as we’ve learned more about this particular virus. We’ve now got evidence from experiments in the lab that show masks trap virus particles, and studies from communities (in Germany and the Czech Republic for example) that show areas that introduced a requirement for face coverings had lower infection rates than neighbouring areas that didn’t.

READ MORE: Covid: Amber country isolation rules in Scotland

We also have some studies that have looked across countries. One study examined the effect of mask wearing on transmission with a dataset from 92 regions on six continents and including a very large survey of more than 20 million people via a world symptoms survey. The researchers took data from these studies and developed a statistical model to link reported wearing levels to Covid-19 cases taking into account other policies, such as stay at home requirements and distancing. They found that where whole populations in a city, region or country were wearing masks public it helped to reduce the reproduction (R) number by around 25%.

A second study compared countries whose populations wore masks in public places within a month of their first reported death from Covid-19 compared with those that introduced this later. The 200 countries that were included had to have good publicly available data that the researchers could access on Covid-19 testing, cases, deaths and policies put in place to address the pandemic. They found that in countries with either cultural norms (a previous tradition of mask wearing) or mask mandates, per-capita deaths from Covid-19 increased by just 16% each week from the first Covid death to May 9th 2020 compared to 62% in countries that introduced masks later, after accounting for a wide range of other factors that might explain these differences.

Studies of this type are not perfect and definitely can’t fully unpick the effect of masks from other elements but taken together with other evidence, their findings are useful.

A further point is that the type of face mask does matter as does the fit. Masks worn as part of personal protective equipment by health professionals, for example, are superior to cloth masks. But even basic face coverings have a role to play. A recent study from Brazil found that simple cloth masks were effective in trapping virus particles breathed out by Covid-19 patients. But practical advice to the public about face coverings is to wear one that fits snugly around your face, including over the nose, under the chin and around the ears without gaps. Those made up of several layers of fabric are better than a single layer.

Masks and face coverings are just one measure among many that can help reduce virus transmission, particularly at a time when Covid-19 infection rates remain high. I can understand that some people still regard being asked to wear one as limiting their personal choices or freedoms. But wearing a face covering in public places is primarily about protecting those around us. We shouldn’t forget that.

Linda Bauld is Chair of Public Health at the University of Edinburgh.