Unfortunately, mandates for mask use in public right now has led to widespread use of homemade masks and mask alternatives. Sure, it’s assumed that wearing such masks reduces the likelihood for an infected person to spread the disease, but many, if not most, of these ad hoc masks have not been tested in practice!
From a public policy perspective, shortages in supply for surgical face masks and N95 respirators, as well as concerns about their side effects and the discomfort of prolonged use, have led to public use of a variety of solutions that are generally less restrictive. These may range from such things as homemade cotton masks or even bandanas!
In general, the term ‘face mask’ governs a wide range of protective equipment with the primary function of reducing the transmission of particles or droplets. The most common application in modern medicine is to provide protection to the wearer (e.g., first responders), but surgical face masks were originally introduced to protect surrounding persons from the wearer, such as protecting patients with open wounds against infectious agents from the surgical team or the persons surrounding a tuberculosis patient from contracting the disease via airborne droplets.
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Remember, face masks are not designed to protect the wearer from inhaling any harmful virus – let’s get this clear once and for all!
Actually, some parties out there have already medically demonstrated that a simple optical measurement method to evaluate the efficacy of masks in reducing the transmission of respiratory droplets during regular speech. We’re pretty sure you can easily find a few on YouTube.
But in a recent, more elaborate proof-of-principle study by the American Association for the Advancement of Science, 14 commonly available masks or mask alternatives were tested. For reference, a control trial was done where a test subject wore no protective mask or covering. Each test was performed with the same protocol.
In every test, a camera was used to record a video of approximately 40 seconds length to record droplets emitted while a test subject is speaking. The first 10 seconds of the video serve as baseline.
In the next 10 seconds, the mask wearer repeated the sentence “Stay healthy, people” five times (speech), after which the camera continued to record for an additional 20 seconds (observation). For each mask and for the control trial, this protocol was repeated 10 times.
The types of masks used in the study.1. Surgical (Surgical mask, three layers) 2. Valved N95 (N95 mask with exhalation valve) 3. Knitted 4. PolyProp (Two-layer polypropylene apron mask) 5. Poly/cotton (Cotton-polypropylene-cotton mask) 6. Max AT (One-layer Maxima AT mask) 7. Cotton 2 (Two-layer cotton, pleated style mask) 8. Cotton 4 (Two-layer cotton, Olson style mask) 9. Cotton 3 (Two-layer cotton, pleated style mask). 10 Cotton 1 (One-layer cotton, pleated style mask) 11. Neck Gaiter (One-layer polyester/spandex, 0.022 g/cm2 12. Bandana (Double-layer bandana, 0.014 g/cm2) 13. Cotton 5 (Two-layer cotton, pleated style mask) 14. Fitted N95 (N95 mask, no exhalation valve, fitted)
In the case of speaking through a mask, there is a physical barrier, which results in a reduction of transmitted droplets and a significant delay between speaking and detecting particles. In effect, the mask acts as a temporal low-pass filter, smoothens the droplet rate over time, and reduces the overall transmission.
For the bandana, the droplet rate is merely reduced very, very slightly, and the repetitions of the speech are still noticeable. The effect of the cotton mask is much stronger. But speech pattern is no longer recognisable, and most of the droplets are removed.
Speaking through some masks (particularly the neck gaiter) seemed to disperse the largest droplets into a multitude of smaller droplets. Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive.
Furthermore, the performance of the valved N95 mask is likely affected by the exhalation valve, which opens for strong outwards airflow. While the valve does not compromise the protection of the wearer, it can decrease the protection of persons surrounding the wearer. In comparison, the performance of the fitted, non-valved N95 mask was far superior.
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So remember… The premise of protection from infected persons wearing a mask is simple: Wearing a face mask will reduce the spread of respiratory droplets containing viruses. And studies strongly suggest that wearing face masks reduces the spread of COVID-19 on a population level and consequently blunts the growth of the epidemic curve. We hope by reading this, you’ll now also have a better idea on what sort of mask you can depend on!
