You’ll notice most of the air purifiers for rooms that we tested have something called a high-efficiency particulate absorbing (HEPA) filter. These can remove 99.97 percent of air pollutants from 0.3 microns in size, which basically means they are really effective at getting rid of the majority of indoor air pollutants.
For context, most dust particles are about five microns in size, and pollen is a staggering 10-1,00 microns – all of which a HEPA filter is able to trap and remove.
Perry tells Live Science that while the most effective air cleaners can remove lots of different types of particles, you’ll never get 100 percent pure air.
He says: "The idea of an air purifier is that it’s designed to get rid of the impurities in your home and neutralize any nasties, such as dust, smells, pet dander, smoke, bacteria and viruses.
“Air purifiers work by having a fan that sucks the dirty air in the home into filters. These then remove any impurities before releasing the cleaned air back into the room. It's important to note, however, that it’s impossible to get rid of all particles, which can live on walls, carpets, bedding and hard surfaces.”