Confused About COVID19 Masks? Let’s Talk

Long before the CDC officially recommended wearing cloth face coverings, people were buzzing about masks. “N95” and “PPE” (personal protective equipment) were two of the first words in our new Corona vocabulary, and by now everyone knows these precious masks are in very short supply.

Meanwhile, the medical community keeps repeating that wearing masks helps prevent sick people from spreading their germs to others, but these masks won’t protect healthy people from catching the exact same germs. Anyone else confused by this? Isn’t it the same mask on a healthy or a sick person? Why would any mask block germs from going out but not from coming in? And WHICH kind of mask are we talking about?

Let’s start with basics:

The COVID19 virus is incredibly small, measuring only 0.1 microns within aerosolized floating particles and up to a 5 microns when traveling in larger respiratory droplets.

For frame of reference:

  • A drop of water is 3,000 microns
  • A average size grain of sand is 250 microns
  • A single strand of human hair is 70 microns (thickness)
  • Oak Pollen is 25-40 microns
  • A red blood cell is 8 microns
  • Most bacteria are about 2 microns

GREAT NEWS:  Properly fitted, airtight N95 respirator masks WORK WELL against COVID19 because they can block out 95% of all particles larger than 0.3 microns.

Surgical masks are designed to block out 95% of particles larger than 3.0 microns (note the factor of 10 difference), which works well for the larger COVID droplets, but not so great for the tiny aerosolized particles. Additionally, surgical masks are loose-fitting, allowing some air flow (with or without viral particles) in and around the sides of the mask. That being said, studies show that in rough terms, compared with the 95% efficacy of N95 masks, surgical masks still manage to be up to 80% effective.

Why are surgical masks ever used if the N95s are better? In general, respirator masks like the N95 were designed to protect the person wearing them from inhaling outside germs, whereas surgical masks were originally designed primarily to keep patients safe from the clinician’s germs. You can see from the filtration size (3.0 microns) that these masks do well to keep the wearer’s mouth/nose bacteria from spreading to the patient. These surgical masks obviously also protect the wearer against splatters or sprays towards their face, but they were never intended to block tiny aerosolized viral particles. Additionally, respirator masks like the N95s are inherently uncomfortable (because of the tight seal), somewhat cumbersome to breathe in, and more expensive than surgical masks. Therefore, outside of a respiratory pandemic, there is no need for these masks to be used for the majority of surgeries, procedures and medical encounters, when the anticipated risk of airborne viral infection is low.

What about cloth? Cloth face coverings vary tremendously by material, design and content (with or without additional filter layers) so not surprisingly, studies show they block anywhere from 10-50% of these same airborne particles. Current best evidence suggests using 100% cotton, at least two layers, and consider inserting a disposable coffee filter with each use.

  • Typical cotton fabric pore size is relatively large: 50-100 microns
  • Average coffee filter pore size: 20 microns (15-25 microns)

At first, you may wonder why these larger pores would block ANY amount of bacteria or viral particles, because basic math tells us a 5-micron COVID respiratory droplet can dance through a 20-micron window, right? But instead of picturing a 20-micron-sized hole, picture more of a 3D crooked pathway or jagged tunnel, created by the layers and thickness of the fabric and filter. Add in moisture, air currents and other physical properties to this viral obstacle course, and we see why cloth barriers are capable of providing some filtration.

Side note: Please do NOT try inserting HEPA filters, because you risk potential inhalation of lung-damaging fiberglass material.

See THIS GUIDE for DIY Mask details.

Every day we learn more about COVID transmission. The highest risks for transmission involve prolonged close contact (~15 minutes) with someone highly symptomatic (fever and cough) or clinical procedures that provoke a cough or sneeze (like doing COVID swab testing or intubating/placing a breathing tube for mechanical ventilation.) Outside medical settings, transmission occurs either by directly breathing in infected respiratory droplets or indirectly through TOUCHING contaminated objects and then TOUCHING your eyes, nose or mouth. Additionally, we know that people can be spreading virus for at least a couple days BEFORE they feel sick, simply by talking and breathing.

Check out this video of “Micro droplets suspending in air” to see a great visual of what we hope to minimize by expanding our use of masks.


Why recommend cloth coverings if they are less effective than surgical masks or N95s?

  1. We have a finite supply of N95s which must be saved for the clinicians involved in the highest risk procedures with the sickest patients.
  2. We are also running short on surgical masks (see #1, and add in people with immune suppression, undergoing chemo, chronic illness, etc.)
  3. We have plentiful supplies to make cloth coverings, and we know they can block SOME percentage of the respiratory droplets, and though not critically studied yet, these barriers may hinder the passage of the viral particles enough to decrease the distance of aerosolized spread. Every little change we can make to reduce possible transmission of this virus moves us forward.

Sneezing and coughing produce extremely high quantities of infected viral respiratory droplets that are ejected with great force, reaching well over six feet if uninhibited. Merely talking emits much lower but still infective amounts of viral particles. Blocking or at least blunting these large droplets with a surgical mask or a cloth face covering helps an infected person decrease their infectivity to others. And remember that wearing a mask in public when you FEEL healthy may be helping others because you may be infected but not have symptoms yet.

If you are truly healthy, will wearing a cloth face cover or surgical mask protect you from COVID19?    No, not by itself. THIS is why we want people to first and foremost- STAY HOME and practice SOCIAL DISTANCING, and then secondarily, WEAR A FACE COVERING when you must go out for groceries. Additionally, any type of face covering gets bonus points for reminding you not to touch your nose and mouth (ditto for wearing glasses and not touching your eyes). Wash your hands before you put on your mask, wash your hands again after you remove and put away your mask, and wash your cloth mask (and swap out coffee filter if using) after each use. Echoing my dear friend and esteemed colleague, Infectious Disease specialist Pranay Sinha MD,  #WearingIsCaring!


BOTTOM LINE: Please wear some type of face covering when you leave your home, but remember, MASKS do not come with SUPERPOWERS to fight off COVID19! Even when you are wearing a mask, please practice strict social distancing and diligent handwashing.

*Thanks to friends Lisa  and Mary Jo for creating these excellent cloth masks for our family! 




3 thoughts on “Confused About COVID19 Masks? Let’s Talk”

  1. Hepa filters from vacuum cleaner bags I understood to possibly contain particles that could damage lungs but many doctors/nurses online have said using Hepa material made for conditioning does not and should be fine to use as long as it is the highest rated
    Is this true?

    • Sorry for delayed reply- apparently it varies by individual product so I can only blanket recommend coffee filters.


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