Most air purifiers have not been tested on humans and are potentially dangerous, — meta-analysis of 700 studies

American scientists from the University of Colorado have concluded from an analysis of 700 studies that portable air purifiers are hardly ever tested on humans and can be potentially dangerous.

Researchers from the University of Colorado Department of Medicine — professor Amiran Baduashvili and professor Lisa Bero notes, that respiratory viruses, such as COVID-19 or influenza, can spread through the air in indoor environments. HEPA filters, ultraviolet radiation, and special ventilation systems, known as engineered infection control, are designed to air purification in the room and prevent the spread of viruses and other pathogens.

Together with colleagues from three academic institutions and two state research agencies, Amiran Baduashvili and Lisa Bero analyzed all studies, evaluating the effectiveness of engineered infection control products, published between 1923 and 2023. In total, the researchers analyzed 672 studies. 

These studies evaluated effectiveness in three key ways. Some studies measured, whether the devices reduced infections in humans, while others — involved animals, such as guinea pigs or mice. The remaining studies took air samples to determine, whether the devices reduce the number of small particles or germs in the air. Only 8% of these studies tested the effectiveness of the devices on humans, while 90% of the studies tested the effectiveness of the devices in empty rooms. 

The researchers found a significant difference between different technologies. For example, 44 studies examined air purification process,  is called photocatalytic oxidation. This process produces chemicals that kill pathogens. However, only one of these studies tested whether this technology kills germs in humans.

Another 35 studies evaluated plasma technologies for killing germs, and none of them involved humans. The researchers also found 43 studies of filters containing nanomaterials designed to both trap and kill germs, and again none of them involved human subjects.

The COVID-19 pandemic has clearly demonstrated, how dangerous transmissible infections can be by airborne droplets. Finding effective ways to remove germs from indoor air can be of enormous benefit to the healthcare system and help limit economic losses in the event of future pandemics.

Companies, that produce portable air purifiers with pathogen-killing technologies, confidently claim the effectiveness of their devices and offer them to consumers for use in kindergartens, schools, hospitals, and offices. However, researchers have found, that most of these devices have not been properly tested for effectiveness. Without hard evidence from human studies, it is impossible to know whether these promises are true.

Amiran Baduashvili and Lisa Bero warns, that some of these air purifiers generate chemicals such as ozone, formaldehyde, and hydroxyl radicals. They kill germs and viruses, but can also harm humans if they inhale these compounds. However, of the 112 studies evaluating many of these pathogen-killing technologies, only 14 tested for harmful byproducts.

More than 90% of all studies analyzed by scientists tested technologies by measuring them, how effectively the air is cleaned from experimental gases, dust particles, or microbes. The idea was that cleaner air should reduce the likelihood of infection. 

However, researchers do not yet know, how accurately these measurements reflect the actual reduction in human incidence. To determine the safest and most effective options, these technologies need to be evaluated for toxicity of by-products and tested in real-world conditions with human participants.

The results of the study are published in the journal Annals of Internal Medicine

Sources: The Conversation; Gizmodo