It’s the Dose — Why Masks Work

What makes a good mask, and how do masks protect us from getting sick?

Masks work by reducing the amount of infectious particles (like a virus) that get into our bodies. While that might seem obvious, the bigger question is how many particles does a mask need to block to be effective?

One important point is that the mask does not need to block all (or nearly all) of them. With a new virus like the coronavirus circling the globe, our immune system actually needs to be exposed to a little bit of the virus in order to recognize it, kill it, and develop long-lasting immunity. So depending on how well our immune system is working, we only run into trouble if we are exposed to “too much”.

Understanding what the body means by “too much” requires a bit of math. Or rather, a picture.

The Dose-Response Curve

Here is a picture of a generalized “dose-response” curve. The numbers are just for illustration — both drugs and infectious particles affect us in this way.

In this example, as you increase the “dose” of viral particles from zero to 100 along the horizontal axis, your chance of becoming sick increases from zero to 100%.

But that increase is not in a straight line — the curve is shaped like an “S” in what’s called a sigmoidal function.

Simple Yet Effective: Single Layer Test

The fact that the dose-response curve is shaped like an “S” means that even simple masks can offer useful protection.

Let’s say you wrap a cotton T-shirt around your face. A 2013 study demonstrated that a single layer of cotton filters out approximately 50% of viral particles.

Now someone coughs as you walk by, and you’re exposed to 60 viral particles. Without any protection, you’d have an 80% chance of getting sick. But with a mask blocking half of them, your chance of getting sick drops to 5%.

While blocking more particles is better, blocking some is still helpful.

Be a Good Neighbor

What if you are infected and shedding viral particles, but don’t know it? If you’re being a good neighbor and wearing even a basic mask, your 60 particle sneeze could be reduced to 30, and the people around you would then only be exposed to an even lower level through their masks.

Everybody wins.

Staying Safe is Simple

  • Wash your hands frequently.
  • Avoid touching your face, especially your mouth/nose/eyes since those places that viruses use to enter your body.
  • Wear a mask — it helps you avoid touching your face, and blocking some particles can make a significant difference.
  • Keep your mask clean. Look for a comfortable mask that allows you to wear it consistently, and wash it frequently.

Easy Masks Can Help

Easy Masks are comfortable, with two-layer construction that provides softness, breathability, and a snug fit. Unlike other cloth or surgical masks where you tend to breathe around the mask, the snug fit on the sides and aluminum nose bridge across the nose and cheekbones ensures that you breathe through the mask.

Filtration testing on a single layer of Easy Masks’ fabric is shown in this chart, with an average overall filtration efficiency of 63% for particles ranging from 0.3 to 10 microns in diameter.

While the coronavirus itself is smaller (0.06 to 0.14 microns), in the wild we are most likely to be exposed to viral particles that have hitched a ride on larger 5-10 micron water droplets.

Interested in Additional Filtration?

Purchase non-woven fabric inserts or download the Easy Masks Insert Template to make free or low-cost filtration inserts to slide between the two mask layers.

Particle Filtration Efficiencies for Easy Masks with our 30 GSM nonwoven fabric inserts are shown in the following chart. These results were generated by RTI International, an independent research laboratory in Research Triangle Park, NC, using an aerosolized salt (KCl) challenge, face velocity of 10.5 cm/sec, and particle sizes ranging from 0.06-0.6 microns.

Check out Smart AIR’s guide to the best materials for a filtration insert, including inexpensive options like shop and paper towels, or cotton fabric.

William (B.J.) Lawson, MD
Co-Founder of Easy Masks

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