Can Air Purifiers Fight COVID or Wildfire Smoke?

This year has given people a lot of reasons to think about the air they breathe. For example, the summer’s West Coast fires released an immense amount of smoke and ash into the air. The resultant poor air quality is worrying for everyone. But even more so for the autoimmune community, who are more likely to have sensitivities and breathing difficulties. The COVID-19 pandemic has inspired discussion about droplet and aerosol transmission. It is increasingly clear that reducing airborne transmission is essential to reduce the spread of the virus. For these reasons and more, many people have turned to air purifiers to reduce pathogens and irritants where they live, work and travel. Therefore, we dive into the specifics of how air purifiers work, and how they can help keep your home free of smoke and coronavirus.

Two types of purifiers: filters and sanitizers

There are two types of air purifiers—filters and sanitizers—though some combine both in one product (1). Filters, most effectively, high-efficiency particulate-arresting (HEPA) filters, remove physical particles like dust, pollen and smoke from the air. This can help alleviate symptoms for people with allergies or sensitivities, as it removes irritants before they can be inhaled (1). HEPA filters function by withdrawing and trapping at least 99.97% of particles that are 0.3 microns in diameter (though some can remove particles as small as 0.01 microns in diameter) within fibers found in the filter (4).

Many air filter models include not only replaceable HEPA filter modules for various particle sizes, but also coarse particulate pre-filters as well as chemical, gas and odor charcoal filters. Pictured is a filter brand Ellen has used at home for 20 years.

a phot of an IQAir filter with 4 filtration stages: particles, carbon and HEPA
IQAir filter.

Sanitizing air purifiers, on the other hand, kill pathogens such as spores, viruses, and bacteria, and most do so via UV light exposure. This can eliminate the root causes for infection and illness (1). Sanitizing air filters function by exposing microbes to UV light, which destroys critical components of these pathogens and inactivates or kills them (2). 

Do filters work against SARS-CoV-2?

Coronaviruses are incredibly small, ranging in diameter between 60 nanometers to 140 nanometers (3). This puts it at the very end of the range of particle size the HEPA filter is able to remove. This means the HEPA filter may not be 100% effective against coronavirus, but can eliminate a large portion (99.94-99.97%) of aerosol-transmitted virus if the filter is run for long periods of time (1). Be sure to choose a filter rated for smaller particles and make sure you have enough filters for every room.

Research has shown that UV radiation exposure destroys the outer protein coat of the SARS Coronavirus, a cousin of the current SARS-CoV-2 virus (2). This suggests that sanitizing air purifiers may be somewhat effective against the coronavirus, though there is no current scientific consensus on the matter, and the efficacy of UV radiation against the virus may also depend on dose and intensity (2). 

Don’t forget that a filter is only one layer of protection against inhaling SARS-CoV-2 viruses in aerosols. Ventilation can be better than filtration if the air turnover is high enough. In hot spots (which at current prevalence includes any enclosed indoor space with people in it), additional protection, such as goggles or face shields, may further reduce your odds of getting infected.

Do these filters work against smoke and ash?

As smoke and ash from wildfires typically do not pose microbial concerns, sanitizing air purifiers may not be the most effective tool to use in this case. HEPA filters, on the other hand, are quite effective at withdrawing particulate pollution from the air and can effectively eliminate smoke pollution within your environment (4). Wildfire smoke particles are typically 0.4 to 0.7 microns in diameter, falling well within the range of particle sizes that can be removed by HEPA filters. We’ve used filters in bedrooms to significantly mitigate the smoke from 2019 and 2020’s Northern California wildfires.

A word about cost

High-quality consumer filters, such as IQAir, can cost hundreds of dollars, even more for central home or workplace systems. For those on smaller budgets, there are good filters available under $100. However, they are smaller and limited in the cubic area they can turnover quickly enough to filter out infectious particles. Here are two guides to less expensive filters: Clean Breathing and Home Air Guides. Don’t forget to budget for replacement filters; HEPA and other purifiers become clogged with particulates and must be replaced. In addition, keep your furnace filter clean. Adding simple fiber filters to furnace output and cold air return can make it easier on your HEPA filter. You can extend the life of all your filters by regularly vacuuming visible dust from the components. Most filters include directions for cleaning.

In addition to autoimmune patients, allergy, asthma, COPD and other chronic respiratory patients, benefit from cleaner personal air. There are a huge number of air filters available today, including small personal ones for your cubicle or on the road.

Air purifiers are not infallible armor against coronavirus or poor air quality. However, they are certainly good tools to incorporate into your environment to make it safer and healthier. Therefore, we hope you found this information helpful and are able to put it to good use. Moreover, check out our post on detoxifying your personal care products for other tips on keeping your personal environment clean and toxin-free!

Stay well!

Written by: Bonnie Feldman, DDS, MBA, Ishita Dubey, BS, Ellen M. Martin


  1. Demarco, C. (2020, September 30). Can air purifiers protect you from COVID-19? Retrieved December, 2020, from
  2. Center for Devices and Radiological Health. (2020, August 11). UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Corona. Retrieved December, 2020, from
  3. Cuffari, B. (2020, July 16). The Size of SARS-CoV-2 Compared to Other Things. Retrieved December, 2020, from
  4. Wong, K. (2017, October 24). What to Know Before Buying an Air Purifier to Clear Wildfire Smoke. Retrieved December, 2020, from


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