Do air purifiers remove smells?

A HEPA filter alone does not remove smells or gases — it only captures solid particles. To remove odours, cooking smells, VOCs or cigarette smoke, the purifier needs an activated carbon (activated charcoal) filter in addition to HEPA. Carbon adsorbs gas molecules onto its surface. A thin mesh of carbon does less than a thick granular carbon bed, so check how substantial the carbon section is before buying.

Are ioniser air purifiers safe?

Most modern ionisers used in reputable air purifiers produce ozone well below the 0.05 ppm limit set by the WHO, and are considered safe for human use. However, birds have much more sensitive respiratory systems and should not be kept in a room with an active ioniser. Some people prefer to disable the ioniser function and rely solely on the mechanical HEPA and carbon filtration — most purifiers allow this.

How Do Air Purifiers Work? The Honest Explanation

An air purifier is fundamentally a fan and a filter. A motor draws room air through the unit, the air passes through one or more filter stages, and clean air is expelled back into the room. That's the core mechanism. The differences between products come down to what filter types are included, how large the filters are, and how fast the fan moves air through them.

Here's what each component actually does.

The Pre-filter

The first stage in most purifiers is a washable mesh pre-filter that captures large particles: dust, pet hair, lint, larger pollen grains. Its job is to protect the more expensive HEPA filter behind it by catching the debris that would otherwise clog it quickly.

You should clean the pre-filter every two to four weeks by brushing it off or rinsing it under a tap. This is not optional maintenance — a clogged pre-filter restricts airflow through the whole unit and reduces filtration performance. It also shortens the life of the HEPA filter, which is the expensive part.

The HEPA Filter

HEPA stands for High Efficiency Particulate Air. A True HEPA filter is independently tested to capture 99.97% of particles at 0.3 microns in diameter. That size — 0.3 microns — is the most penetrating particle size (MPPS). Particles both smaller and larger than 0.3 microns are actually easier to capture; HEPA filters are tested at the hardest size first.

What this means in practice: a True HEPA filter will capture pollen (10-100 microns), most bacteria (1-10 microns), dust mite allergen (1-10 microns), mould spores (2-10 microns), fine dust (PM2.5, below 2.5 microns), and most combustion particles. It will not capture gas molecules, which are far smaller than 0.3 microns.

H-grade HEPA filters are more precisely specified. H11 captures 95% at MPPS. H12 captures 99.5%. H13 — the grade you see in quality purifiers — captures 99.97% at MPPS and 99.95% overall. H14 captures 99.995%. For domestic use, H13 is the relevant benchmark.

HEPA-type or HEPA-style are marketing terms with no regulation or standard. They can mean almost anything. If a product listing doesn't specifically say True HEPA or quote an H-grade, assume the filtration performance is below True HEPA specification.

The Activated Carbon Filter

Activated carbon (also called activated charcoal) works by adsorption — gas molecules in the air bind to the enormous surface area of the carbon's porous structure. A single gram of activated carbon can have a surface area of 500-1,500 square metres depending on its grade.

The carbon layer handles what HEPA cannot: gases, VOCs (volatile organic compounds), cooking smells, pet odours, cigarette smoke, off-gassing from new furniture and paint fumes. It does not capture solid particles — that's the HEPA filter's job.

The amount of activated carbon matters. A thin mesh or sheet of carbon saturates relatively quickly and stops working. A granular or pellet-based carbon bed with meaningful weight to it lasts longer and performs more consistently. Cheaper purifiers often include just enough carbon to mention it on the spec sheet; better ones use a substantial carbon section.

The carbon filter cannot be regenerated at home. Once saturated, it needs replacing.

The Ioniser (or PlasmaWave, or Plasma Technology)

Many purifiers include an ionisation stage as an additional filtration mechanism. An ioniser generates negative ions that attach to airborne particles, causing them to clump together and either fall out of the air onto surfaces, or become large enough to be captured by the HEPA filter.

Some purifiers — Winix's PlasmaWave, for instance — use a bipolar ionisation method that generates hydroxyl radicals. These react with and neutralise airborne bacteria, viruses and VOCs at a molecular level, rather than just making particles fall to the floor.

The ozone concern. All ionisation technologies produce trace amounts of ozone as a byproduct. The question is how much. Reputable manufacturers keep this well below the WHO guideline of 0.05 ppm and often seek third-party ozone safety certification. Budget ionisers from unknown brands are more variable. If you have birds as pets, avoid ionisers entirely — birds cannot tolerate even trace ozone levels.

Most purifiers allow you to switch the ioniser off while keeping the HEPA and carbon filtration active. If you'd rather not have any ionisation chemistry, you can opt out.

UV-C Light

Some purifiers include a UV-C bulb that claims to kill bacteria and viruses as air passes through. In principle this works — UV-C light does inactivate pathogens. In practice, the exposure time as air passes a UV-C bulb at fan speed is usually too brief for meaningful inactivation, and the bulb contributes minor ozone. In tests, UV-C stages in consumer air purifiers add little measurable benefit beyond the HEPA and carbon filtration.

It's not harmful, but it's not a reason to choose a purifier either.

What Air Purifiers Cannot Do

Remove settled allergens. Purifiers clean airborne particles. Dust mite allergen, pet dander and pollen settle onto carpets, sofas, mattresses and curtains, where a purifier can't reach them. Regular hoovering with a HEPA-filtered vacuum and washing bedding at 60°C address settled allergens.

Fix condensation damp or mould. Air purifiers can catch mould spores floating in the air, but they don't address the moisture conditions that cause mould to grow. If you have condensation on windows or mould on walls, you have a humidity or ventilation problem — a purifier treats the symptom but not the cause. See our comparison of air purifiers vs dehumidifiers for what to use where.

Replace ventilation. Fresh outside air contains far lower concentrations of indoor pollutants than recirculated room air. Where practical, opening windows is effective. A purifier is most useful in situations where opening windows isn't practical — high outdoor pollen counts, living on a busy road, or overnight when it's too cold.

Reduce humidity. A purifier moves and filters air; it doesn't remove moisture. If your home is damp, you need a dehumidifier.

Now you know how they work. See our full air purifier roundup for specific product recommendations, our HEPA filter guide for more on filter grades, and our honest take on whether air purifiers are worth buying if you're still deciding.