Air purifiers – owned by one in four Americans – are rarely tested on humans and could actually do more harm than good, a new study suggests.  

A team of researchers from the University of Colorado Anschutz Medical Campus went through nearly 700 studies on air-cleaning devices meant to improve indoor air quality and hinder the spread of viruses and other disease-causing microbes.

They found that only eight percent of these studies evaluated the devices’ effectiveness on humans, while the majority, over 90 percent, conducted tests in empty spaces.

In the instances where tests were conducted, most were laboratory-based, using test subjects like guinea pigs or mice, or involved collecting air samples to assess if the devices decreased particle or microbe levels in the air.

Additionally, the research indicated that some devices emit harmful byproducts, such as ozone or formaldehyde, which could lead to issues like permanent lung damage, asthma, or even cancer.

Ozone can be produced by air purifiers either deliberately, in machines designed to use ozone gas to eliminate pollutants, or inadvertently as a byproduct. Formaldehyde may result when ozone or ionizers interact with other airborne chemicals.

Of 112 studies looking at air purifiers that used chemicals to kill microbes, only 14 of these tested for harmful byproducts. 

‘This is a stark contrast to pharmaceutical research, where safety testing is standard practice,’ the researchers state.  

Air purifiers are rarely tested on humans and could actually do more harm than good, a new study suggests (stock image)

Because ozone is a respiratory irritant and not suitable for indoor environments, the California Air Resources Board suggests avoiding ozone generators and recommends choosing purifiers equipped with HEPA filters instead.

Meanwhile, ozone has been found to react with existing chemicals in the air to create additional toxic pollutants, most notably formaldehyde – a known carcinogen – and ultrafine particles (UFPs).

UFPs are microscopic airborne pollutants that can deeply penetrate the lungs, enter the bloodstream, and travel to all organs, leading to inflammation, cardiovascular diseases, and increased mortality. 

Formaldehyde is a toxic gas found indoors and outdoors that causes irritation of the eyes, nose, and throat, coughing, and wheezing at higher concentrations. 

The health effects of formaldehyde can be worsened by ultrafine particles, which can carry the chemical and other toxic compounds deeper into the body.

The University of Colorado researchers worked with colleagues across three academic institutions and two government science agencies to analyze every research study evaluating the effectiveness of air purifiers published from the 1920s through 2023. 

This totaled 672 investigations.

They said they found ‘substantial variation across different technologies’. 

For example, 44 studies examined an air cleaning process called photocatalytic oxidation, which produces chemicals that kill microbes, but only one of those tested whether the technology prevented infections in people. 

Another 35 studies evaluated plasma-based technologies for killing microbes, and none involved human participants. 

They also found 43 studies on filters incorporating ‘nanomaterials’ designed to both capture and kill microbes – again, none included human testing.

Off the back of their findings, the researchers suggest that consumers should proceed with caution when investing in air cleaning devices.

The US air purifier market size was estimated at $4.5 billion in 2024 and is projected to grow 7.2 percent from 2025 to 2030

Analysts from Grand View Research say the rising demand for air purifiers in the US can be attributed to the ‘rising health awareness and the increasing importance of indoor air quality’ (stock image)

Lead researchers, Amiran Baduashvili and Lisa Bero, conclude: ‘The gap between marketing claims and evidence of effectiveness [of air purifiers] might not be surprising, but there is more at stake here. 

‘The safety of these products should be the baseline requirement before they are widely deployed.

‘The idea is that cleaner air should mean lower chances of infection. But when it comes to air cleaning, researchers don’t yet know how strongly these air measurements reflect actual reduction in infections for people.

‘More real-world, human-centered testing is needed to identify which devices are both effective and safe for schools, hospitals, and workplaces.’

The US air purifier market size was estimated at $4.5 billion in 2024 and is projected to grow 7.2 percent from 2025 to 2030. 

Analysts from Grand View Research say the rising demand for air purifiers in the US can be attributed to the ‘rising health awareness and the increasing importance of indoor air quality in residential, commercial, and industrial facilities’. 

The Covid-19 pandemic also caused a surge in air purifier demand as consumers looked to protect indoor air quality against airborne viruses.