It feels like the story of masks has come a long way, and the conversation now is not about whether or not masks are effective as an additional preventative measure against COVID, but which type of mask will be the most practical and effectiveness for everyday individuals needing to go to the shops, boarding public transport, or even protesting.
In this article, we are going to be comparing surgical masks with PM2.5 pollution masks with air filters. We are not going to be considering the respiratory masks and the plain cloth based masks because they are at the extreme ends of the effectiveness spectrum. Obviously, the N95 or N99 respiratory grade mask is going to be the most effective - they are used by doctors on the front line. The cloth based masks offers some basic protection, but does not come with any certified filtration properties against fine particles.
In the middle of the spectrum are surgical masks and anti pollution masks. Not a great deal is written comparing the two styles of masks, and this article will do a deep dive analysing every aspect of these masks and finding out what are the best use cases for each style of masks.
First, what is a surgical mask?
According to the CDC, a surgical mask is " loose-fitting, disposable device that creates a physical barrier between the mouth and nose of the wearer and potential contaminants in the immediate environment." Other names for surgical masks include: medical masks, dental masks, isolation masks, medical procedure masks, or simply face masks.
Typically, surgical masks are made made of three layers: a middle layer of extra fine glass fibres or synthetic microfibres covered on both sides by acrylic bonded parallel-laid or wet laid nonwoven fabrics. They are commonly referred to as 3-ply or three-ply, meaning that it is made of three layers joined together.
A surgical mask is a tool used in the medical profession, and its main function is to prevent the spread of respiratory infection from the medical practitioner to the patient. According to the US Food and Drug Authority, a surgical mask helps to block large-particle droplets, splashes, sprays, or splatter that may contain germs (viruses and bacteria), keeping it from reaching your mouth and nose. Surgical masks may also help reduce exposure of your saliva and respiratory secretions to others.
However, the surgical mask is not designed to protect the wearer from airborne particles and aerosols from others. It is loose fitting, has visible gaps/leakage around the side of the face, and is not certified to filter particles to the N95 or N99 standards like the respiratory masks.
The intended use case of a surgical masks is that its a one-off for a medical procedure, and for the mask to be discarded after each patient encounter.
How good are surgical masks at blocking viruses and other respiratory particles?
Scientific studies and evidence suggests that it is indeed effective at blocking viruses and tiny airborne particles, from the wearer of the mask. Recently studies have also showed that it does also protect an uninfected wearer, but only to an extent.
A recent and relevant scientifically peer reviewed study was published by Hong Kong University in April 2020. In this study, 246 patients with seasonal human coronaviruses, influenza viruses and rhinoviruses participated in an exercise whereby the patients exhaled breaths into a device that could capture and measure the amount of viral particles entered at different sizes, at >PM5 (5 microns, referred to as respiratory droplets), as well as fine aerosol particles at <5 microns in size (referred to as aerosol particles). Half of participants were randomised to wear surgical masks, the other half not.
The result showed that the the surgical mask was generally effective at filtering respiratory droplets. At >5 microns, the typical size of respiratory droplets within 2 metres, face masks were able to reduce the detection of viruses from 30% (unmasked) to 0% (masked) for corona viruses, 26% (unmasked) to 4% (masked) for influenza virus and 28% (unmasked) to 22% (masked) for rhinoviruses. At <5 microns, face masks were able to reduce the detection of viruses from 40% to 0% for corona viruses, 35% to 22% for influenza virus and 56% to 38% for rhinoviruses. See table below.
The interesting part of the study was that while the surgical mask is very effective against respiratory droplets, it was significantly less effective at capturing aerosols. However, the authors pointed out that the viral load of aerosols were found to be relatively lower.
Overall, the authors concluded that "this has important implications for control of COVID-19, suggesting that surgical face masks could be used by ill people to reduce onward transmission."
There are three important critiques to be made from the above assessment.
- The authors did not look at how effective the surgical mask was at filtering respiratory droplets and aerosols exhaled by other people (not the wearer) at different distances
- The authors did not look at the effectiveness of mask filtration from the standpoints of a social environment, such as simulating a restaurant or concert.
- The study did not look at COVID-19 specifically, and so are inferring from other corona viruses.
Realising this, the Hong Kong University is putting together a new paper that looks at the effectiveness of surgical masks in an environment where COVID-19 exists in the air. To do this, the scientists had a cage of hamsters infected with COVID-19, and another cage of uninfected hamsters. The uninfected hamsters were then exposed to air flow from an infected hamster's cage, with or without surgical masks blocking the airflow.
The study has not been published or peer reviewed yet but has produced preliminary results that showed:
- When the uninfected hamsters were exposed to the air flow from an infected hamster's cafe, 66% of the Hamster became infected with COVID-19 within 7 days
- When the airflow from the infected hamster's cage went through a surgical mask placed at the infected hamster's cage, the number of hamsters in the uninfected cafe that became infected with COVID-19 dropped to 16.6%.
- When the airflow from the infected hamster's cage went through a surgical mask placed at the uninfected hamster's cage, the number of hamsters in the uninfected cafe that became infected with COVID-19 dropped to 33.3%
The study also highlighted the importance of viral load. Even if infected, the use of surgical masks were found to significantly reduce the viral load of COVID-19. The hamsters that became infected without mask had more severe symptoms than those hamster that were infected through masks.
This is however one study and science is moving fast in the field, specifically looking at effectiveness against COVID-19. Another recent study looked at different settings in the community and healthcare sectors that applied difference interventions with or without surgical masks. The study found that in the community, "masks appeared to be more effective than hand hygiene alone, and both together are more protective".
What can be concluded, is that if everybody in an environment wore surgical masks, the chances of transmission of viruses, particularly corona viruses and influenza viruses can be reduced to negligible levels. Even if infected people are not wearing masks but the uninfected people are, the risk of infection can still be significantly reduced. Finally, the wearing of masks can reduce the viral load of COVID-19, leading to milder symptoms even if infected.
This is exactly the strategies adopted by places such as Hong Kong and Taiwan, where the use of surgical mask by the mass population is prevalent and promoted by the government.
Who is the surgical mask suitable for?
The surgical mask is convenient, easy to dispense and offers substantial protection at a lower initial entry point price than pollution masks. It is suitable for the following situations/people:
- People who want to keep things simple, and who do not want to deal with maintenance such as washing and replacing of filters
- People who are not living in polluted areas, and therefore do not require the mask to have anti-pollution functionality
- People who want a little more breathing comfort, as the surgical mask is generally more breathable and has air gaps on the side
- There is no shortage of surgical masks in the consumer's country. If there is a surgical mask shortage, then arguably those masks should be reserved for use by medical professionals.
The one major downside of surgical masks is that it is disposable and therefore has a very short lifetime and are very wasteful to the environment. The typical use case for surgical mask is 1-2 days before it has to be discarded. Further, surgical masks can lose its filtration functions if it comes into contact with liquid.
One way to extend the lifetime of surgical masks and therefore preserve valuable resources is to use a surgical mask cover. It can double the lifetime of surgical masks and also protect it from rain. Wearing a mask cover can also provide additional protection and is more comfortable on a wearer's sensitive skin.
What is a PM2.5 Anti Pollution mask?
A PM2.5 pollution mask is a mask that is designed to filter out particulate matter in the air. These particulate matter can include dust, soil, pollen and chemicals. Viruses can also be captured by anti pollution masks like any other particles.
There are many different categories and names for PM2.5 masks, such as pollution masks, air filter masks, cycling pollution masks, smog masks, filtered face masks and reusable dust masks.
The PM2.5 refers to Particular Matter, and the 2.5 refers to the size of the particular matter that the mask is able to filter. Therefore, PM2.5 refers to particulates that are at least 2.5 microns in size. While most pollution particles are 2.5 microns or larger, corona viruses are much smaller than pollution particles, at between 0.06 to 0.14 microns in size.
Therefore, it is not a given that the wearing of a PM2.5 mask will provide adequate protection against COVID-19. There are particular technical details to look for within PM2.5 pollution masks.
First of all, there are generally two styles of pollution masks.
- The PM2.5 filter is sewn inside the mask and cannot be replaced
- The PM2.5 filter is removeable and can be replaced
There are pros and cons associated with each style. If the filter is sewn inside, it provide a tighter seal than one that can be replaced, leaving less gaps for particles to go through. However, these types of masks have a shorter shelf life and the filters lose effectiveness after 3-4 months and have to be discarded. It is therefore much more wasteful and worse to the environment.
Now let's turn to the PM2.5 filter. Not all filters are made equal. Filters are typically certified to a standard which measures filtration %, which is usually measured in terms of the % of particles filtered at 0.3 microns in size (so much smaller than 2.5 microns that it is purported to filter). Most filters have 4-5 layers, with an activated carbon filter layer to capture tiny particles.
In terms of certifications, most pollution mask providers offer N95 certification or equivalent, such and KN95. Please refer to our blog post about what is involved in a N95 certification. Essentially, the filter is certified to filter out 95% of particles at 0.3 microns in size, in laboratory conditions. This is referred to as the Particle Filtration Efficiency. There are also other certifications for Anti Bacterial Efficiency, Viral Filtration Efficiency and Breathing Resistance.
Some companies can even offer filters with a N99 rating, which can filter out 99% of particles at 0.3 microns in size.
How good are PM2.5 pollution masks at blocking viruses and other respiratory particles?
There are no published peer reviewed scientific papers that we are aware of that looked at the effectiveness of PM2.5 pollution masks at filtering viruses. That is understandable as the main purposes of the masks are to filter pollution, not to protect against viruses such as COVID-19.
However, there are inferences that can be made from other studies.
A 2013 study in the journal Disaster Medicine and Public Health Preparedness looked at the filtration efficiency of a range of fabrics. To measure the filtration efficiency, the researchers made home made masks and sprayed virus into the air in the direction of the different masks.
The results can be seen in the table below, in the column Bacteriophage MS2:
As expected, surgical masks performed the best, at 89% filtration efficiency. However this was followed by the vacuum cleaner bag at a respectable 85% filtration efficiency. The remaining fabrics offer a degree of protection but drop off significantly.
So although there hasn't been any scientific studies looking at PM2.5 pollution masks at filtering viruses, a well fitted pollution mask with N95 or N99 certified filters should in theory perform as well, if not better than the surgical mask at capturing viral particles.
Who is the PM2.5 pollution mask suitable for?
A PM2.5 pollution mask with either N95 or better still N99 certifications for its air filters, could offer performance that are comparable to surgical masks, in terms of protecting others or yourself against COVID19 infection. Look for N95 or N99 grade face mask online, instead of just searching for PM2.5 masks.
What is clear is that PM2.5 pollution masks do offer substantially more protection against regular cloth masks made from cotton. The pollution mask is in many countries easier to purchase than surgical masks, are washable and reusable, and many come with replaceable filters. It is suitable for the following situations/users:
- People who want to make an investment for a long lasting mask, who is prepared to maintain it through regular washing and/or replacement of filters
- People who live in areas where they are exposed to high levels of pollution. In effect the mask can be used to serve two purposes, to protect against both pollution and COVID19
- People who want more variety in the appearance of the masks. PM2.5 anti pollution masks come in all forms of different colours and patterns.
- People who want a tight fit and seal of the mask. Pollution masks usually come in a range of sizes to suit individuals from children, women to large adults.
- People who live in countries where surgical masks are in short supply and do not want to divert resources from the medical front line.
In summary, the jury is still out on whether the surgical mask or the PM2.5 pollution mask is more effective at filtering respiratory droplets airborne viral particles. However, there are distinct use cases for each type of mask and are suitable for individuals in different situations.
Craft Cadence face mask with nanofiber technology
Craft Cadence is pleased to announce that our new V2 ViralOff face masks will come with both a sewn in N99 certified nanofibre filter, and the option to insert removable N99 certified nanofibre filters to further prolong the life of the mask. This is the first mask in the world (that we are aware of) to have both options available.
We are also happy to make available on request:
- The FFP3 (N99) certified report of our nanofiber filters
- An internal wash report which shows that the filter loses 2% of the filtration efficiency after 10 washes. We will look to gain third party certification of the after wash filtration efficiency of the filter in the future.
- Our Polygiene ViralOff laboratory results and certification, showing that our outer layer eliminates 99% of viruses within 2 hours, including SARS-Cov-2.