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Mask wearing in schools and indoor public places has become a hotly debated topic across the world, but research shows face coverings do help reduce the spread of Covid-19.

To what extent masks offer protection depends on the quality and type, however. As the UK struggles to contain the Omicron variant, the government has advised that everyone aged 12 and over must wear a face mask in indoor public venues including secondary school classrooms and on public transport - rules that have reignited debate about which type to choose.

In the initial stages of the pandemic, the UK public was urged not to buy surgical-grade masks used by health professionals, because of shortages of such protective gear. Surgical-grade masks are now more widely available and offer greater protection than standard cloth coverings.

But government regulations still “say little about the best kind of protection”, wrote Clare Horwell, professor of Geohealth at Durham University, in an article for The Guardian. The current guidance dates back to a time when Covid-19 was primarily thought to spread “within large droplets, emitted when someone sneezed or coughed”.

Yet we now know that the virus is mainly transmitted through tiny aerosol particles that can travel “metres on an infected person’s breath” and linger in the air for hours, Howell added.

Research has found that the masks that offer the highest level of protection to the wearer and people around them are FFP2 masks, with a similar type of respirator mask known as the N95 available in the US. Surgical FFP1 masks are also highly effective.

Studies suggest that FFP1 masks offer at least 80% efficiency in blocking aerosol particles. The World Health Organization has cited studies showing that the filtration systems of FFP2 and N95 masks are 94% and 95% effective respectively, if properly fitted. However, they tend to be non-reusable, so can be an expensive option.

FFP1, FFP2 and N95 masks not only protect the wearer but “dramatically reduce risk to others too”, wrote Cotswolds-based GP Mark Porter in an article for The Times. But he advised against the use of respirator masks with exhaust valves, on the basis that while they make breathing easier for the wearer, “they also increase aerosol production, potentially putting those around you at risk”, he said.

In Germany, the use of either an FFP1 or FFP2 masks while at work, in shops or travelling in public transport has been mandated since April. These masks are also required in all public places in France.

Experts say that if high-quality respirator masks are unavailable, medical-grade surgical masks are the next best option.

Dr Peter Chin-Hong, a specialist in infectious diseases at the University of California-San Francisco, told Quartz that “a baseline should be a surgical mask”. He added that “even in the hospital, I’m mainly wearing a surgical mask”.

True medical-grade masks are made of “three layers of nonwoven fabric typically made from plastic”, with filtration layers “sandwiched” in the middle, said CNN.

These masks will generally offer more protection than cloth masks alone, but “less than a tightly fitted respirator”.

Although cloth masks have been found to be less effective than wearing respirator or surgical masks, they still offer a higher level of protection than using no mask at all.

Ashley Styczynski, an infectious disease fellow at Stanford University who recently co-authored a large-scale study looking at the efficacy of different types of masks, told Bloomberg that typically, cloth materials block “10%-30% of aerosol-sized particles that contribute to airborne spread of SARS-CoV-2” - far less than respirator masks such as FFP2s and N95s.

Styczynski and her colleagues at Stanford performed a study across 600 villages in Bangladesh, where they provided surgical masks to some of the villages and cloth masks to others to assess their real-world efficacy.

“When considering both types of masks together, we found a significant reduction in Covid-19. When we looked at each of the mask types separately, we found that surgical masks were especially effective in reducing Covid-19, though there was more uncertainty for cloth masks,” she said.

“It may be that we didn't see an effect of cloth masks on Covid-19 because fewer people were given cloths masks. However, both cloth and surgical masks significantly reduced Covid-like symptoms, suggesting that cloth masks offer some protection.”

Raina MacIntyre, head of the biosecurity research programme at the University of New South Wales in Australia, told Quartz that a “high-performing cloth mask” can be fashioned to effectively block droplets, using a combination of cotton/linen and polyester/nylon – to resemble the performance of surgical protection.

US public health agency the Centers for Disease Control and Prevention has said that the fit of either cloth or surgical masks can be improved by knotting the straps and tucking the sides. The rule of thumb is that a mask is generally a good fit if the wearer can feel warm air coming through the front of the mask as they inhale and exhale.

Current UK government guidelines say that face visors or shields should only be worn in addition to a face covering, but not alone. According to official advice, “face visors or shields do not adequately cover the nose and mouth, and do not filter airborne particles”. 

The US Centers for Disease Control and Prevention also does not recommend using face shields instead of masks, as it is “unclear how much protection shields provide” said Mayo Clinic. “If you must use a face shield instead of a mask, choose one that wraps around the sides of your face and extends below your chin,” the agency advised. 

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