Now should I wear a mask? Can I wash them?

Person putting on a face mask, specifically an N95 respirator. Does this practice protect us and others from SARS-CoV-2?
Should I wear a mask? How can I safely reuse them?

CDC recently recommended everybody wear a cloth mask in public. San Francisco announced Friday a general requirement for the public to wear face masks. To be safe and comply, let’s

  1. Discuss why the change in general face mask recommendations.
  2. How to safely reuse face masks. Can we wash them? We want to use methods that (1) kill coronavirus and (2) don’t compromise the integrity of the face mask.

Today let’s start with the question should I wear a mask now? And why do the recommendations keep changing?

Why do face mask recommendations keep changing? Why should I wear a mask now?

The foundation of medicine lies in “risk benefit ratios”. Recommending widespread mask usage is no different, and I made a graphic to summarize this particular risk benefit comparison:

Diagram showing rationale behind "should I wear a mask". The risk and benefit ratio of widespread mask usage is explained.
My diagram explaining the rationale for mask usage.

To understand how this risk-benefit is determined, recall virus spread is categorized in three transmission methods:

  1. Contact: virus lives on surfaces, and we touch those surfaces and then touch the mucous membranes of our face
  2. Droplet: virus lives in water droplets that are expelled from our nose and mouth when we cough or sneeze, and those droplets come in contact with the susceptible parts of our bodies to infect us
  3. Airborne: very small suspensions of virus persist in the air for extended periods of time when we breath, cough, or sneeze, and come in contact with the susceptible parts of our bodies to infect us

What is the risk benefit ratio based on these transmission methods? What is the ratio and why should I wear a mask?

Benefits:

  • Likely reduce spread from contagious people.
    • Respiratory droplets can spread from talking (in addition to coughing and sneezing). A wet cloth covering the face can minimize the spread of these droplets.
    •  In an enclosed space this can minimize spread of droplets, particularly from people actively coughing and sneezing.
    • While likely beneficial, surgical and cloth masks are hardly bulletproof, so they are NOT a substitute for physical distancing. Note this study found little difference when COVID-19 patients coughed with surgical masks, cloth masks, and no mask (!).
  • May possibly protect healthy people
    • We have little evidence to directly support this. The barrier (however incomplete) may possibly reduce droplets and (less likely) airborne particles from reaching our nose and mouth.
  • Note that our eyes are still susceptible. Unless you’re wearing a full face shield you are still quite susceptible to infection.
  • In other viral illnesses, masks may possibly reduce transmission. In those cases, surgical masks may be more effective than home made masks. We must be careful in extrapolating that general idea to our specific COVID-19 and PPE scenario.

Risks:

  • PPE shortage
    • Frontline medical workers perform hazardous procedures that do have high risk of droplet and airborne SARS-CoV-2 spread. Frontline workers in particular need N95 masks!
    • If frontline medical workers need to reuse masks they risk spreading virus to different patients.
  • Incorrect use may lead to self-inoculation and possibly risking others (see my previous post)

When the risk-benefit ratio favors benefit of widespread mask usage

Sick individuals should always wear a mask in public, but when should everybody wear face masks? Consider if:

  • The virus is prevalent enough, then even the small benefit of wearing a face mask (if healthy) may justify its use.
  • Virus is spread considerably through droplet and airborne routes (where masks may be effective).
  • There is significant “asymptomatic spread”. Read: lots of spread from people before they develop symptoms. This is true because nearly have of infections may happen just before symptoms start!
  • Virus continues to shed even after people have recovered. We are still learning more about this, but it has been observed ins COVID-19 (see my post here).

Conclusion: the general public should wear masks, particularly in crowded and enclosed areas

Wearing a mask is less for the person wearing the mask. It is more to protect those around the person wearing the mask. This is all the more important because nearly half the spread may come from people before they have developed symptoms. Remember, the incubation period lasts roughly 5 days, and contagion appears maximal around day 4!

Washing and reusing face masks

Because we should now be wearing masks in public, even if healthy, we will shortly run into worsening mask shortages. To be safe, we need to find strategies to reuse our masks safely. We’ll discuss the following strategies:

  • UV light
  • Hydrogen peroxide (vaporized)
  • Alcohol
  • Disinfecting wipes
  • Soap and water
  • Sunlight
  • Microwaves
  • Steam

Most of these strategies have potential, but are only safely performed in hospitals. We will discuss soon!

Stay safe and keep sheltering in place!


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The information provided in this post in intended for general education. It is not medical advice. While I make every effort to provide the most up-to-date information, please note that new data is continuously becoming available and may change the conclusions I present here.

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