Masks explained

By Stavros Christoudias, MD, FACS


One of the most common questions I get asked is on the different types of masks and the different purposes for the different types.

There are two basic functions of masks and you can separate them by each function:

  1. To protect everyone else from your contaminants coming out of your mouth, which happens with this virus when you breathe, speak, cough, and sneeze—listed in order from least amount of contamination to the highest and most forceful blast o’ virus—the sneeze.
  2. To protect you from everyone else, these are generally termed a “respirator”, is rated by NIOSH, and needs a tight seal against your face to work. There are other nuances to an N95, But the most important thing to know is they act as a filter, catching the virus in it, and preventing them from reaching your airways as you breathe in. The problem is that the virus eventually covers the outside of the mask, and they themselves can become sources of contamination if not handled correctly or used within NIOSH guidelines. Anyone who wants to know more about an N95 respirator Can PM me and I’ll point you in the right direction.


So, let’s look at each mask and their performance on the above basis:

Surgical Masks

Surgical Masks filter out approximately 60-70pct of viral “spray” out of your mouth. These are completely open on the sides, so they offer only SOME protection to the wearer from infection of true airborne viruses. The problem with COVID-19 is that WE STILL DO NOT KNOW FOR SURE IF IT IS COMMONLY AIRBORNE. Its this lack of knowledge that has created the confusion and conflicting recommendations on how protective these are. So, these very much protect everyone else but are weak protection for the wearer. These work best if worn by “everyone”, and will help us “flatten the curve” the more they’re worn in public.


N/R/P 95/99/100 respirators


These are all considered “gold standard” protection for the wearer, but ironically, they are considered poorer protection from everyone else from the wearer. They filter out 95pct or more of the virus out of the air. However, in terms of filtering out your viral spray, some of these respirators are even worse than surgical masks! So often a wearer of an N95 respirator will still have to wear a surgical mask OVER the N95 (as I do during surgery). Without that surgical mask over it, if I were only wearing an N95 respirator, I’d have a very high likelihood of contaminating the surgical field! This aspect of the N95’s function (suppression of viral spray) is greatly worsened on N95 masks with valves. (I.e. the valves let out unimpeded air, likely full of virus). The letters in front denote how resistant they are to oil contaminants
(N=Not resistant to oils, R=Somewhat Resistant to oils—some gets through, and P= Oil Proof—completely blocks oils.) The number of values describe what percentage of contaminants it stops. 95pct and above is considered good enough to prevent COVID infection.



Almost no protection to the wearer (less than 10pct filtration, if any at all), however, offers minimal protection/suppression of your “viral spray”, reducing it by roughly 10pct. The protective/filtration function is improved for larger molecules (e.g. smoke) if it’s wet. However, it doesn’t help with COVID, because whatever water captures the virus is most likely to work its way into your airway.

The way that all these masks actually work best in preventing COVID, is that it stops you from touching your mouth or nose, and inoculating yourself.

So let’s summarize in COVID context:

• Surgical masks—good for everyone else, marginally protective for the wearer.
• N95 respirator—good for the wearer, moderate to poor for everyone else—varying greatly by type.
• Bandana- only better than wearing nothing.

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