The face mask is one of the best defenses we have against the COVID virus. All face masks, however, are not alike. Here we explore the history of medical masks and discriminate the most effective from the less effective.
History and Purpose of Surgical Masks
In the 1860s, Louis Pasteur proposed that microorganisms caused spoiling of wine, beer, and milk and invented the process of pasteurization to avoid the “diseases” of wine.1 He believed that microorganisms also caused animal and human disease. Shortly thereafter, Joseph Lister2 began using carbolic acid to inactivate germs on surgical wounds and instruments.
Finally, in 1897, after learning from bacteriologist Carl Flügge that respiratory droplets carry culturable bacteria, Polish surgeon Johann Mikulicz began wearing a mask in the operating room. French surgeon Paul Berger, began doing likewise.3
Early surgeons knew that a majority of the respiratory droplets were expelled through talking. Consequently, they made it routine to avoid talking in the operating room, instead using hand gestures to request instruments. This was quite prescient. Less prescient was that they ignored the respiratory droplets potentially coming from the nose and consequently often wore the mask only covering the mouth.
The year 1919 saw the patenting of reusable cotton surgical masks. Then, in the 1960s, single use, disposable surgical masks began replacing the cotton varieties.
In the early 1900s, masks were considered important only in protecting the surgical patient from the exhalations of physicians and nurses. This changed with the Manchurian plague of 1910 and the influenza pandemic of 1918, which saw the mask as protecting physicians, nurses, and civilians from the exhalations of potentially infected patients.3
Types of Masks
The two most popular masks are the “surgical mask” and the N95 mask.
The “surgical mask” is the familiar rectangular mask with horizontal pleats, white inside and colored (usually green or blue) outside worn by securing an upper and a lower pair of ties or ear loops. The white and colored layers sandwich a middle layer of microfibers that obstruct particles mechanically and/or hold them with an electrostatic charge.4
On the other hand, the N95 mask or N95 respirator is a roughly cup-shaped device, sometimes with a vertical fold, and of the same color (usually white) both inside and outside, with a middle layer of microfibers that obstruct particles mechanically and/or hold them by an electrostatic charge.
Differences between the Two Masks
Layers
-- The surgical mask has different inner and outer layers. The outer layer is fluid resistant as additional protectionfrom infected droplets contacting the mucous membranes of the nose or mouth of the wearer.
-- In the N95 mask, the same materials compose the inside and outside layers.
Fit
-- The surgical mask does not conform well to the face and permits unfiltered air to enter and exit around the mask. This is more pronounced on inhalation when the mask tends to collapse on the wearer’s face.
-- The N95 mask has improved conformance to the features of the face and improved stability to reduce air flow in and out around the mask.
Original Purpose
-- The surgical mask was intended to protect the patient from the surgeon’s exhalations and the surgeon from irrigating fluid splashes during surgery.
-- The N95 mask descends from masks intended to protect workers from particle inhalation.
Filtration
-- Surgical masks differ in filtration but most effectively filter particles of 3.0 micron size and some effectively filter particles of 0.1 micron size.
-- N95 masks filter 95% of particles size 0.3 microns; this is the origin of their name N95. For comparison, the COVID-19 virus has a reported size of 0.05 to 0.2 microns.5
Effectiveness
-- N95 masks are considered more effective than surgical masks in part because their shape reduces leaks around the mask.
For this reason, the N95 masks are recommended for healthcare workers and prioritized to them by the World Health Organization (WHO)6 and the Centers for Disease Control (CDC)7.
Correct Wearing of Masks
-- The World Health Organization has produced this excellent infographic on the correct wearing of masks.8
Other Face Coverings
Although it would seem that any face covering is better than no face covering, this is seldom the choice, as surgical masks, if not N95 masks, are usually readily available and they are certainly the most efficacious.
Valved N95 Type Masks
These are distinctly inferior or surgical or N95 masks. The valve closes on inhalation so that inflowing air is filtered. It then opens on exhalation. This is appealing as it makes exhalation easier and reduces moisture and heat buildup inside the mask. However, it fails to protect others from the wearer’s exhalations. The mask may also generate a false sense of effectiveness since it looks like an N95 mask.
Homemade Masks
Homemade masks of cotton or T-shirt material vary in effectiveness directly as the number of layers of cotton in the mask and inversely as the number of times the mask has been laundered. Regardless, however, the best homemade masks are inferior to the surgical or N95 masks.9
Neck Gaiters
Neck gaiters fared even worse in effectiveness experiments.9 Of course, the stretchy construction makes for ease in pulling up or down, but it also creates more permeability in the fabric. Certainly, being able to see through the face covering when it is held up to the light is an indication of the covering’s ineffectiveness.
Bandanas
At the bottom of the effectiveness list are bandanas according to experiment.9
These permit easy escape of virus-laden droplets both through and out the bottom of the covering.
Face Shield
Th transparent face shield was never designed to be respiratory protection for the wearer
or proximate persons. The wide openings at the bottom and sides permit broad inflow and
outflow of unfiltered air. However, since virus particles gain access to the body through th
mucous membranes of the eyes as well as those of the nose and mouth, the face shield
was designed to protect the eyes from splashes containing microbiological contaminants.
Conclusion
Until widespread inoculation with COVID-19 vaccine can be implemented, surgical and N95 masks are some of the best weapons against the corona virus. To achieve this goal, they must be chosen over less effective options and used correctly, certainly until we can view this epidemic as passed.
Thomas Falasca, DO FACA FACPM
References
1 Louis Pasteur. (2020, November 29). Retrieved December 3, 2020, from https://en.wikipedia.org/wiki/Louis_Pasteur
2 Joseph Lister. (2020, November 29). Retrieved December 3, 2020, from https://en.wikipedia.org/wiki/Joseph_Lister
3 Strasser, B. J., & Schlich, T. (2020, May 22). A history of the medical mask and the rise of throwaway ... Retrieved December 3, 2020, from https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(20)31207-1.pdf
4 Surgical mask. (2020, November 28). Retrieved December 5, 2020, from https://en.wikipedia.org/wiki/Surgical_mask
5 Severe acute respiratory syndrome coronavirus 2. (2020, December 04). Retrieved December 5, 2020, from https://en.wikipedia.org/wiki/Severe_acute_respiratory_syndrome_coronavirus_2
6 Mask use in the context of COVID-19: Interim guidance, 1 December 2020. (2020, December 01). Retrieved December 5, 2020, from https://apps.who.int/iris/handle/10665/337199
7 Centers for Disease Control (CDC). (2020, August 08). Personal Protective Equipment: Questions and Answers. Retrieved December 5, 2020, from https://www.cdc.gov/coronavirus/2019-ncov/hcp/respirator-use-faq.html
8 World Health Organization (WHO). (2020, December 01). When and how to use masks. Retrieved December 5, 2020, from https://www.who.int/emergencies/diseases/novel-coronavirus-2019/advice-for-public/when-and-how-to-use-masks
9 Dockrill, P. (2020, August 10). Simple New Experiment Reveals Which Face Masks Are Best at Blocking Droplets. Retrieved December 5, 2020, from https://www.sciencealert.com/simple-low-cost-experiment-reveals-which-face-masks-are-best-at-blocking-droplets
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