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The question of whether or not wearing a facemask “works” is incredibly complicated. It may not seem so at first, but let me list some of the specific questions contained in that broad question. We need to consider different kinds of masks – cloth, surgical, N95. We need to consider who is wearing the mask – someone known to be infected, someone who is well, and in what setting – out in public or in the presence of those known to be sick. We also need to operationally define “work”. We can measure reduction in the spread of the virus, in droplets, in aerosolized particles, and also in different conditions (breathing, coughing) and at different distances. We can measure deposition of virus on surfaces. We can also measure transmission of actual disease, both the chance of spreading and of catching specific illnesses. And of course, all of these questions need to be addressed with each specific infection, and so prior research may not apply perfectly to COVID-19. And further, we need to compare the efficacy of wearing a mask to the real-work effectiveness of intending to use a mask.

It should not be surprising, therefore, that we do not have all the answers to these questions specifically for COVID-19. What we have are slices of research with different results and therefore you can look at the preliminary evidence we do have and come to different conclusions. The CDC and the WHO, in fact, have done this. Here is the CDC recommendation:

CDC recommends wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain (e.g., grocery stores and pharmacies), especially in areas of significant community-based transmission.

CDC also advises the use of simple cloth face coverings to slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others. Cloth face coverings fashioned from household items or made at home from common materials at low cost can be used as an additional, voluntary public health measure.

Cloth face coverings should not be placed on young children under age 2, anyone who has trouble breathing, or is unconscious, incapacitated or otherwise unable to remove the mask without assistance.

The cloth face coverings recommended are not surgical masks or N-95 respirators. Those are critical supplies that must continue to be reserved for healthcare workers and other medical first responders, as recommended by current CDC guidance.”

And here is the WHO:

If you are healthy, you only need to wear a mask if you are taking care of a person with COVID-19.

The WHO recommends masks for those who are symptomatic or known to have COVID-19, and those exposed to people who are sick, but not for the healthy out in public. The guidelines are actually not that far off from each other, but there is that one difference.

What does the scientific evidence actually say? I will start with some recent studies dealing specifically with COVID-19. There is a recent study which is getting a lot of press but I think has limited implications. The study involved four subjects with COVID-19 coughing with several mask types, and without any mask, onto petri dishes. The masks themselves were also swabbed after coughing. They found the masks did not prevent spread of the virus through coughing (for every mask type, some virus still made it onto the petri dishes). They also found virus on the outside of the masks but not the inside, which is a bit counterintuitive. They speculate that airflow around the mask may be depositing the virus on the outside. Some outlets have reported this finding as suggesting that masks “don’t work” but that cannot be concluded from this one study.

First, they did not test the efficacy of the masks without coughing. They did not test the efficacy of the mask for others exposed to the coughing. And they did not test the factor of distance – perhaps masks reduce the safe distance to avoid transmission. They also did not test to see if masks reduce the amount of virus in the environment of the sick. The study really only tested the filtering ability of the masks for coughing and at short distance.

Another recent study, however, found that surgical masks (which are much less effective than the N95 masks) are somewhat effective:

Surgical face masks significantly reduced detection of influenza virus RNA in respiratory droplets and coronavirus RNA in aerosols, with a trend toward reduced detection of coronavirus RNA in respiratory droplets. Our results indicate that surgical face masks could prevent transmission of human coronaviruses and influenza viruses from symptomatic individuals.

More importantly, there is a recent systematic review of 19 trials, which concludes:

The study suggests that community mask use by well people could be beneficial, particularly for COVID-19, where transmission may be pre-symptomatic. The studies of masks as source control also suggest a benefit, and may be important during the COVID-19 pandemic in universal community face mask use as well as in health care settings. Trials in healthcare workers support the use of respirators continuously during a shift. This may prevent health worker infections and deaths from COVID-19, as aerosolisation in the hospital setting has been documented.

My summary of all this is that, first, we don’t have definitive evidence to know exactly what the effect of mask wearing is in every setting. But we can make some reasonable extrapolations from the data we have. First, for hospital workers, they really should be using the N95 masks, and surgical masks if the former are not available. For the public the cloth masks may be of some benefit, both in spreading and receiving the virus. However, the benefit is likely to be modest. It should not be considered full protection, but just a way to reduce the chance of spread a little bit.

But I think perhaps the biggest factor in terms of the general public use of face masks is the intention to treat consideration – how are people actually using their face masks. The data shows that the modest decrease in risk of spread is only there if people use their masks consistently and properly. When they don’t, what little protection there is vanishes.

Now I am going to introduce some personal anecdotal information, through my observations over the last two months. I am still seeing patients, with maximal precautions, which includes everyone who comes into the clinic wearing a face mask. I have also been deliberately observant when I am out in the public (for essential services). What I have observed is most people not using their masks properly. Many people have the mask below their nose, which is essentially useless. Or the mask is on loosely. But far and away the greatest violation of protocol is that people touch their mask or temporarily remove their mask, and frequently adjust their mask. This is understandable. Non health-care providers are not used to wearing masks. They were not trained how to use them. The masks can be uncomfortable, and whenever you cannot touch your face, it itches. So people are constantly fidgeting with their masks.

This may be worse than useless. We now have data of virus deposition on the outside of face masks, so touching your mask is a good way to spread the virus. Also, there is the “false sense of security” issue. People may feel they don’t have to be a rigorous with social distancing because they are wearing a mask.

So here, then, is my bottom line. Sure, wear face masks whenever you are out in public or have to be exposed to other people – but wear the mask properly, don’t touch or adjust it, don’t take it off or lower it even briefly. Further, understand this is only modest protection. It may statistically help reduce the spread of the pandemic, but it is not total protection. So you still have to adhere to strict recommendations to avoid spread – physical distancing and hand washing being the most important. Also, if you are sick, you can apparently cough the virus through your mask, so still cough into your elbow and not at other people or onto the environment. But most importantly, if you think you may be sick, self-isolate. A mask is not adequate protection for others.

So wear the mask properly, but act as if the mask does not work.

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Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.