an air purifier sucks in dirty air at the bottom and releases clean air from the top

Air Purifiers - Part 1: What Are Air Purifiers Supposed To Do, Exactly?

Back in December, I purchased an air purifier. And I’ll be honest, I was a skeptic: do they actually do anything? I’ve now spent the past 7 months using it alongside a personal air quality monitoring device (while also spending even more time in my house for 4.5 months of protective self-protection/self-isolation more-or-less), so I figure it’s a good time to dig back into the age-old question (at least for me): do air purifiers actually do anything for asthma?

In this article, we’ll look at what air purifiers do and the research. In part 2, I’ll share my own experience.

What are air purifiers supposed to do?

To find out if air purifiers actually do anything, because recall, I am somewhat of a skeptic around these things (despite buying one), let’s look at what air purifiers are actually supposed to do. Fortunately, the folks at Good Housekeeping (who I feel should be reliable despite the fact that I am probably not qualified as a Good Housekeeper myself), did a piece on this back in March. They state that:1

“Air purifiers usually consist of a filter, or multiple filters, and a fan that sucks in and circulates air. As air moves through the filter, pollutants and particles are captured and clean air is pushed back out into the living space."

In my case, this living space is my bedroom.1

The filter used is often what is known as a HEPA, or high-efficiency particulate air, filter. Even back to a double-blind study in 1990, HEPA filters have been researched as a means to help improve asthma and allergy symptoms.2 This study stated the HEPA filter on average decreased particulate matter greater or equal than 0.3 microns by 70%.2

What do air purifiers actually do?

It may be that my asthma specialist seemed indifferent toward air purifiers when I inquired those many years ago, because the evidence on their efficacy appears mixed. A study published in 2010 notes the following of HEPA air filters:3

  • “May be effective for removing pet allergens” and they appear to be effective in decreasing cat and dog allergen when used in uncarpeted rooms "or in conjunction with HEPA vacuuming of carpeted rooms.” A Cochrane review notes the evidence is not strong enough to recommend use where pets are present in the home of a person with a pet allergy.
  • They do not appear effective at reducing dust mites and mold, however, a small study demonstrated a decrease in airborne particulates that could improve symptoms in those with dust mite allergy.

Evidence for improvements in clinical outcomes is not generally convincing

  • One study showed when used with other strategies to mitigate pet allergies, including bedding encasements and keeping cats out of the living area, the air purifier did not show considerable evidence for efficacy
  • Another showed HEPA filtration improved airways hyper-responsiveness (a clinical measure) but not symptoms.
  • Air filters were found to be most effective when used in conjunction with vacuuming.

Now, I would anticipate personally that HEPA air filtration devices may have gotten quieter since 1990 or 2010, but I would not think the mechanics of how they work would be much different now, a decade later. But I decided to take a look.

Does disease severity play a role?

A 2020 meta-analysis notes it is possible that disease severity plays a role—but it is not clinically significant:4

"In patients with mild to moderate disease, we observed small (not reaching the minimum clinically important difference) but significant improvements in the [Asthma Quality of Life Questionnaire] scores and [fractional exhaled nitric oxide] levels. This effect could possibly be stronger in patients with severe asthma than in those with mild to moderate asthma."

A study also notes use of a HEPA air purifier may have greater impact on asthma-related quality of life in those with asthma receiving GINA Step 4 therapy or higher who remain poorly controlled despite this treatment.4 The meta-analysis, again, concludes that future research needs to be done to make a recommendation on the usefulness of air purifiers. Because of course, we are no further ahead than we were in 1990 (before I was born), right?

In my next article, I’ll share my own experiments and observations about life with the hum of an air purifier.

If you use an air purifier, have you found it helps your asthma or allergy symptoms? Share in the comments below!

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This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

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