They're one of the must-have home devices, but do air purifiers work? What are the potential health benefits of having one in your home and how do they actually work? To help answer these questions, we’ve sought advice from experts to better understand the effectiveness of these domestic appliances.

In addition, we explore whether a medical-grade air purifier could reduce the causes of asthma and allergies, as well as manage the symptoms associated with these conditions. And, if the findings prompt you to think about purchasing one, our guide to the best air purifiers on the market, as well as in-depth reviews on top models like the Blue Pure 211+ air purifier and KOIOS EPI810 air purifier, can help you choose a device that's right for your home.

Do air purifiers work?

Air purifiers promise to clean the air in your home by removing airborne pollutants, such as dust, pollen and smoke particles. If you are thinking of using a purifier to tackle air pollution caused by traffic, it’s worth noting that some are fitted with carbon filters, which are designed to capture gases. But do air purifiers work or are these claims simply marketing hype?

Most air purifiers available today consist of a filter, or multiple filters, and a fan that draws in and circulates air. As air travels through the filter, particles are captured and the clean air is pushed back out into the living space. As a result an air purifier’s filters, which are typically made of paper, mesh or fiber, have to be replaced regularly in order to maintain efficiency. The frequency with which they need to be replaced will depend on the type of purifier and the amount you use it, although some appliances come with washable and reusable filters.

An alternative type of air purifier uses ionizers instead of filters to create a static charge around particles, effectively reducing the number that are circulating in the air. If this is an option you are considering, make sure the ionizer doesn’t produce ozone, as this can irritate lungs and further aggravate asthma symptoms.You might also come across ultraviolet light (UV) filters, which claim to destroy biological impurities such as bacteria or mold spores. However, it’s important to be aware that some bacteria are UV-resistant.

So while air purifiers work by filtering some pollutant particles out of the air, allergens such as dust mites or pet dander are not able to be captured when embedded in furniture or carpets. Similarly, there’s little indication that those without carbon filters can remove gaseous pollutants that may accumulate from paints or cleaning products.

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What are medical-grade air purifiers?

For an air purifier to be termed ‘medical-grade’, it should be able to stop the smallest particle types, like viruses, from getting through. Air purifiers featuring High Efficiency Particulate Air filters (or HEPA filters) have the ability to capture the vast majority of airborne particles that measure 0.3 microns in diameter. As with other purifiers, a fan draws air into a HEPA filter, which captures particles within multiple layers of netting or mesh – these are most often made from interwoven glass fibers or synthetic materials.

Particles are trapped by HEPA filters in three different ways:

Diffusion – as smaller particle types, such as viruses, move around erratically they eventually hit and stick to the filter Interception – as air flows through the filter, the particles contained in the air flow touch the filter and stick to it Impaction – as larger particle types collide with the netting, they crash and stick to the filter The industry standard for an air purifier with HEPA filters is that it should be able to remove at least 99.97% of particulates measuring 0.3 micron in diameter in a laboratory setting. However, when used in a real-life setting, an air purifier’s ability to work this effectively is likely to be far less as new pollutants are constantly emerging.

Do doctors recommend air purifiers?

We’ve looked at how air purifiers work, but are they effective when it comes to cleaning indoor air? Dr John O Warner OBE – Emeritus Professor of Paediatrics, National Heart and Lung Institute, Imperial College, London – said that, quite simply, the overwhelming majority have very little impact on improving air quality. "Many of them suck in air and blow it out again. That said, those with HEPA filters can catch particles down to a very small size, but at the same time they create vortices that stir up any dust that happens to be around them."

He commented that, because of the turbulence they create, someone would have to be situated a very short distance away from an air purifier for it to have any real impact. In addition, factors such as location, flow rate and how long it’s operating for will all affect how well an air purifier works.

And while the team at Asthma UK report that some people find their asthma symptoms are alleviated by air filters, they are quick to point out that these appliances can’t remove all allergens and that even a few left behind can trigger a reaction.

"For an air purifier to pull out particles you’d have to stir them all up from the floor, soft furnishings and anywhere else, and of course they would accumulate again fairly quickly. Often, better ventilation is achieved by having a door or window open to allow the air to flow," said Dr Warner.

What else can air purifiers do?

While an air purifier can work to remove some indoor pollutants, there is very little medical evidence that they will directly improve your health. However, allergy or asthma sufferers might find an air purifier with a HEPA filter is of use when it comes to removing fine airborne particles.

Related: Do air purifiers help with allergies?