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Broadly speaking, there are three main types of air purifying technology: Hepa filters, carbon filters and ionisers. But how do they purify your air and which type will work best for you?

Hepa filters remove solid particles from the air, while carbon filters trap chemical fumes. Ionisers take dust and pollen out of the air but many don't trap it and are therefore less effective. Here's what you need to know.

In the air purifier market, there are a number of competing brands and technologies that make a lot of impressive-sounding claims. However, even if a product claims to remove 95% or 99% of airborne pollutants, the reality is that it won’t clean your air to that extent.

But if you buy the right kind of air purifier for your needs, it should make a noticeable difference to the air quality in your home.

They can be a good purchase for people with a sensitivity to dust or dander, or to people who suffer from hayfever. They can also help your home air quality if you live near a main road.

How do air purifiers work?

Most air purifiers use fans to draw air inside and pull it through a series of filters, before venting the cleaned air back into the room. A purifier may use different types of filter, separately or in combination. You may see Hepa-grade filters or activated charcoal filters mentioned.

Other air purifiers use ionic or electrostatic technology.

Hepa filters

Best for: dust and pollen, traffic pollution

A Hepa (high efficiency particulate air) filter is the industry standard. It works to remove particle pollution from the air. It must trap 99.97% of particulates that are 0.3 micrometres or larger. To give you an idea of scale, there are 10,000 microns (micrometres) in a centimetre.

Large particles of dust and pollen affect the nose and throat, causing hayfever symptoms. A Hepa filter should not only help with this but also remove the smaller particles that get past these defences and can be dangerous to our lungs.

PM10 particles, which are 10 microns wide, can make their way into our lungs and PM2.5 particles can get right in the alveoli and cause damage. That’s why a Hepa filter is important.

But the truth is that some of the air will get sucked through gaps in the machine and won’t be filtered, which is why a well-made purifier can make a difference. An air purifier is an appliance where engineering is all-important and unfortunately that makes effective air purifiers expensive.

An air purifier will only filter the air in your home that reaches it, so you should also look for a purifier with solid fan power as well.

Charcoal filters

Best for: removing paint, solvent and other chemical fumes from the air

Charcoal filters, also known as carbon air filters, can remove gaseous pollutants, including VOCs, from the air. They trap them in a bed of charcoal. This means that they're also effective at removing odour. However, they can’t remove solid particles including mould, dust or pollen.

VOCs or volatile organic compounds are a group of carbon-based chemicals that evaporate in the air at room temperature. Some are harmless, others can be extremely harmful to our health. Examples include benzene (which can come from glue, cleaning products, adhesives and smoke) and formaldehyde (from cleaning products, space heaters, smoke), which are carcinogenic.

Products that emit these gases in our homes include:

  • air fresheners and scented products, including candles and deodorant 
  • cleaning products
  • paints and varnish
  • adhesives
  • aerosol sprays
  • cosmetics
  • stored fuel
  • solvents
  • dry-cleaned clothing

Charcoal filters must be replaced regularly as they will become completely ineffective once saturated.

Ionic purifiers

Not recommended for: hayfever sufferers, as they won't take pollen and dust out of circulation

Ionic purifiers release negatively charged ions, which attract positively charged ions in dust, allergens and bacteria. This increases the weight of the particles, which then drop to the floor and can be vacuumed up. Ionisers don’t use filters at all, which cuts down on expense and maintenance. They are also quiet.

However, they will not remove gases or VOCs from the air. And, unless they are equipped with fans to pull in the air, they will only attract particles from directly around the machine and will make a very limited difference to the overall air quality in your home.

They also release small amounts of ozone into the air. There is some disagreement over whether or not the levels produced are high enough to prove dangerous, but many asthmatics say it worsens their symptoms.

Electrostatic purifiers

Best for: dust and pollen, traffic pollution

Electrostatic purifiers are a form of ioniser. They use an electrical charge to attract particles to a plate, so they capture the dust, rather than just removing it from the air. This type of purifier is quite efficient, removing 95.3% of airborne particles. One of its benefits is that you don’t need to replace the filters. However, you will need to wash them out every 4-6 months.

Like other ionising purifiers, they only work on particles, not gases.

Which type of purifier is right for you?

Air purifiers remove two types of air pollutants: particulate matter and VOCs. Ionic purifiers and Hepa filters will only remove particles. Carbon filters will only remove VOCs and other gases.

If you're worried about fumes from chemicals in your home, you should purchase a purifier with a carbon filter. 

If you suffer from hayfever or sensitivity to dust and dander, you should look for an air purifier with a good quality Hepa filter, or a fan-assisted ioniser if you prefer that technology. These filters will also help with traffic pollutants and dangerous particulate matter from open fires and other forms of combustion.

We've tested and would recommend Dyson's range of air purifiers. They are not cheap but if you're suffering from road pollution, pollen OR dust, and it's exacerbated by the heat, a good purifier will give you some relief.

Dyson's Pure Cool purifying tower fan is currently available from the Dyson website for £499. This model is a good choice for purifying the air in an entire room. You can read our review for more information. If you're looking for a smaller device, the Pure Cool Me is a personal air purifier, which we also reviewed and rated highly. It's available for £299 from the Dyson site.

Want to read more? Find out how a humidifier can help with the symptoms of COVID-19 or get advice on how to improve the air quality in your home