Do N95 Masks and Respirators Really Work?


3M N95 mask

N95 respirators, commonly called N95 masks, are air filters worn on the face to capture tiny pollution particles before they can reach the sensitive tissue in your lungs. The effectiveness of N95 masks is controversial, and evidence on both sides of the issue is far from comprehensive.

Through my work as a biomedical researcher, I have access to sophisticated air quality measurement equipment, so I ran my own battery of tests to determine if N95 masks are effective medical equipment or a false sense of security.

N95 is an efficiency rating from the National Institute for Occupational Health and Safety (NIOSH) that means the N95 mask filters out 95% of (N)on-oil particles larger than .3 microns (.00003 cm). The masks are commonly worn to protect users from dust while working and from air pollution in many large cities, most notably in China[1].


Pollution Health Effects:

Air pollution has been shown to increase the risk of stroke, heart disease, lung cancer, and both chronic and acute respiratory diseases. At high levels of pollution, those with asthma can be triggered into having asthma attacks. With air pollution, smaller particles are more harmful because they travel further into your lungs before being trapped.

Particulate matter that is 2.5 microns or smaller (PM2.5) is the most dangerous to our respiratory health because they are small enough to make it all the way into the deepest parts of our lungs.

High PM2.5 concentrations can cause acute symptoms like respiratory irritation, shortness of breath, coughing, sneezing, and runny nose. Those with asthma may be triggered into having an attack. Long-term exposure to PM2.5 pollution has been linked to increases in cardiovascular and respiratory related hospital and emergency room visits. Studies also suggest links to heart disease, chronic bronchitis, reduced lung function, lung cancer, and death[2].

PM10 is another measure of air pollutants that measure between 2.5 and 10 microns in size. Typically, there are fewer PM10 than PM2.5 particles in the air as the larger, heavier pollution falls out more quickly.

Stations all over the world monitor air quality in real time. To find out the air quality in your area, search for your city on

What makes a good N95 Mask?

N95 Mask Used to Remove Old Fiberglass InsulationThis N95 mask was used to tear out old fiberglass for hours in an enclosed space. It still works very well as a filter, despite appearances. The dirt on the inside of the mask comes from leaks around the edge of the mask, not penetration through the filter.

In order to filter particles out of the air, the air actually has to pass through the N95 mask meaning the mask-to-face seal has to be good. I discovered that air passing directly through a clean filter is almost completely free of PM2.5 particles (99.95% reduction). Almost all of the dirty air comes through at the mask-to-face seal.

Most N95 masks come with elastic straps that go around your head and an adjustable nose clip to create the best possible seal. The 8511V mask that I recommend takes it one step further and features a soft lip that broadly contacts your face, plugging small gaps in the seal.

N95 Masks Filter:

  • Dust
  • Pollution
  • Bacteria
  • Viruses
  • Allergens

N95 Masks Do Not Filter:

  • Oil based substances
  • Gases

Vented masks are a necessity for comfort, and non-vented masks are only slightly cheaper. The vent is a one-way valve that allows your breath to exit without condensing on the inside of the mask or fogging up your glasses. While it does not make the N95 mask a better or worse filter, it is far more comfortable with the vent.

Buy  non-vented masks if you are using it to keep your sickness to yourself. While the masks are not designed to catch stuff coming out of your mouth, they will still filter any air that goes through them. With a vent installed most of the air coming out of your mouth does not pass through the filter.

Beards are the enemy with any respiratory mask, but particle reduction is the name of the game. An N95 mask does not have to block all particles, so even if there is a poor seal, any air flowing through the filter means cleaner breathing for you.

    How Long Can I Use the Same N95 Mask?

    The N95 masks seem to be disposable considering they are lightweight and come in packs of 10, but there are no instructions for duration of use. I measured the air velocity and filtration effectiveness before and after running 4000 cubic feet of dirty air through a piece of mask the size of a penny. The mask was black with dirt, but the air flow rate only slowed a little and the filter was still catching over 98% of PM2.5. These N95 masks clog with dirt and wear out VERY slowly, so even if they are black and nasty they will still filter air just fine.

    N95 Up Close and In Depth:

    Dirt Particles Trapped in an N95 Mask FilterDirt particles (lighter grey) being captured by an N95 Mask Filter.

    For those of you wondering what exactly is going on at the microscopic level, I took an up-close look with a Field Emission Scanning Electron Microscope (FE-SEM). If you're not sure what that is, it's a really powerful microscope that can make things look up to 80,000 times larger.

    I used it to look at the dirty N95 masks to see how they trapped particles. Many filters work by having holes that are smaller than what they want to filter out. Since the N95 mask is used to filter out extremely tiny particles and it's not necessary to filter out every single speck, it takes a different approach. The filter is a tangled mass of jumbled up fibers laid on top of each other. As air passes through it, the particles in the air have a good chance of bumping into one of these fibers. When they do, they get stuck. Because the N95 works this way, the filter does not clog easily and will still work nearly as well even when it's dirty.

    The Bottom Line:

    The 8511 vented mask is the best I have found, and one of the top rated N95 masks on Amazon. The filters work well for catching dust, pollution, bacteria, and viruses. They also stay effective despite long, intense usage. If you are purchasing a mask to prevent others from catching a sickness that you have, make sure you buy a mask without a vent.

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    About Peter Oldani - Author of Inside First Aid

    About the author

    Peter Oldani graduated college with a B.S. in biomedical engineering, worked as an EMT to gain hands on experience in emergency medicine and completed active shooter training as part of New York State’s initiative to prepare civilian organizations for disaster response.