Most Air Cleaning Devices Have Not Been Tested On People

A new review of nearly 700 studies on portable air cleaners found that over 90% of them were tested in empty spaces, not on people, leaving major gaps in evidence about whether these devices actually prevent infections or if they might even cause harm by releasing chemicals like ozone or formaldehyde. The Conversation reports: Many respiratory viruses, such as COVID-19 and influenza, can spread through indoor air. Technologies such as HEPA filters, ultraviolet light and special ventilation designs -- collectively known as engineering infection controls -- are intended to clean indoor air and prevent viruses and other disease-causing pathogens from spreading. Along with our colleagues across three academic institutions and two government science agencies, we identified and analyzed every research study evaluating the effectiveness of these technologies published from the 1920s through 2023 -- 672 of them in total.

These studies assessed performance in three main ways: Some measured whether the interventions reduced infections in people; others used animals such as guinea pigs or mice; and the rest took air samples to determine whether the devices reduced the number of small particles or microbes in the air. Only about 8% of the studies tested effectiveness on people, while over 90% tested the devices in unoccupied spaces.

We 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. We also found 43 studies on filters incorporating nanomaterials designed to both capture and kill microbes -- again, none included human testing.

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