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Do air purifiers filter and kill viruses and bacteria?

Many air purifiers claim to filter out and even kill viruses and bacteria, including the COVID-19 coronavirus, but is that true?

air purifier with a woman sleeping
Last updated: 04 August 2020

Need to know

  • Many air purifiers can actually trap and even kill viruses and bacteria, but only the ones that are in the air at the time
  • A HEPA filter can be surprisingly effective at trapping viruses, but it won't kill them
  • An air purifier is not a substitute for good hygiene such as washing your hands and cleaning hard surfaces

We've been asked by several CHOICE members whether an air purifier can help keep their home clear of germs, including the COVID-19 coronavirus.

The short answer is yes, but only to a limited degree. Many air purifiers actually are capable of trapping and even killing viruses, but they can only be expected to trap a small percentage of germs in the air in a typical home. It's far more important that you simply keep up the usual hygiene practices: washing your hands, cleaning hard surfaces, and of course, trying to avoid bringing germs into your home in the first place.

Let's look at how effective an air purifier filter can be when it comes to trapping a virus.

HEPA filters and the coronavirus

HEPA (high efficiency particulate air) filters claim to filter particles down to 0.3 microns (0.3 micrometres, or 300 nanometres). 

Most viruses vary in diameter from a mere 20 nanometres (that's 0.02 microns, or 0.00002mm) up to 400nm (0.4 microns); some are bigger still. A typical coronavirus is about 100 nanometres, or 0.1 microns, in diameter. That puts the coronavirus, and most other viruses, well below the particle size that a HEPA filter can claim to trap.

However, studies show that such tiny particles can still be trapped by a HEPA filter, and in fact the filter has a good chance of trapping most such miniscule particles that it encounters. Because particles of this size tend to move in random directions (rather than in a straight line), there's a good chance they'll still make contact with the filter fibres as they pass through it, and become attached to the filter surface just like a larger particle such as dust.

Small aerosol particles from a cough or sneeze can remain airborne for hours. An air purifier with a HEPA filter can help to remove these.

So it is very possible that an air purifier with a HEPA filter may trap any airborne viruses, including the COVID-19 coronavirus, that happen to pass through it. But it won't necessarily kill the virus. Even if trapped, the virus may stay alive on the filter surface for several hours or even days. However, the virus will probably eventually die there, unless you happen to remove the filter in the meantime, which might release the virus back into the air or onto your skin.

But an air purifier can only filter particles from air (obviously), and only from the air that they actually suck in. Viruses are also likely to be found on a person's skin, or left on a hard surface that the person has touched, and there's nothing the air purifier can do about that. Even if a person coughs or sneezes and the expelled fluids contain viruses, the larger droplets are likely to settle to the floor or other surfaces rather than remain airborne for a long time. But there is evidence that the small aerosol particles from a cough or sneeze can remain airborne for hours, and these particles can also carry viruses. An air purifier with a HEPA filter can help to remove these small particles from the air.

Other filters: photocatalytic, carbon and more

  • Photocatalytic air purifiers can also trap and kill bacteria and viruses, as they are caught and potentially broken down by the electrostatic and oxidisation effects of the ions generated by this type of filter.
  • Ultraviolet (UV) light is also a good steriliser, and some air purifiers have a UV sterilising feature. But usually a virus or bacteria has to be exposed to UV light for several minutes to be destroyed, and it's not clear that is the case inside many air purifiers. If the UV is used to sterilise a filter that has trapped the germs, that could be very effective; but if the air is simply passed through a UV light, it may not be exposed for long enough to be of much use.
  • Catechin-based filters may also have antiviral properties, but we haven't seen many models with this type of filter. Catechin is a plant extract with antifungal and antibacterial properties.
  • Carbon filters and other types of filters can be good for trapping odours, volatile organic compounds and other pollutants, but are unlikely to trap germs.

Again, though, any of these filters or sterilisers can only trap a virus that has actually been airborne and passed through the air purifier; it can do nothing about viruses on a person or on a hard surface.

There are more effective ways to protect yourself

In summary: an air purifier may be able to trap and even kill some of the viruses that happen to be in the air, so it can be a useful supplement in keeping your home's air virus-free. 

But viruses are also found on skin, in bodily fluids or are left on hard surfaces after human contact. Your first and best options are still the same as before: avoid crowded spaces, minimise unnecessary contact, clean any hard surfaces that people often touch, and regularly wash or sanitise your hands.

We care about accuracy. See something that's not quite right in this article? Let us know or read more about fact-checking at CHOICE