Ionisers and ozone air purifiers: are they safe?
In one line: ionisers charge particles so they clump and settle rather than filtering them out, and some produce ozone as a by-product. Ozone is a lung irritant, so intentional ozone generators aren't recommended for occupied rooms. A filter-based purifier is the safer, better-evidenced choice.
Ioniser vs filter — the difference
A conventional purifier physically traps particles in a filter and removes them from the room (see HEPA vs MERV-13). An ioniser instead emits charged ions that make airborne particles stick together and to surfaces, so they fall out of the air or land on walls and furniture — they're not captured and removed, just relocated, and can be re-disturbed later.
Where ozone comes in
Some ionising and "plasma"/"activated oxygen" devices generate ozone, either deliberately or as a by-product. Ozone can react with pollutants, which is how these are marketed — but ozone itself is a respiratory irritant that can worsen asthma and irritate the lungs at elevated indoor levels. Health and environmental bodies advise against using ozone-generating devices in occupied spaces.
Rule of thumb: if a purifier is marketed as "filterless", "ozone", "activated oxygen" or "plasma", check whether it emits ozone. For everyday clean air, a mechanical filter (HEPA or MERV-13) is the safer, more effective and better-evidenced approach.
What to look for instead
- A genuine mechanical particle filter — true HEPA (H13+) or MERV-13.
- Stated ozone-free operation, or certification such as CARB (California) which limits ozone emissions.
- For gases and odours, activated carbon — not ozone.
Next step
Looking for a safe, ozone-free unit? See filter-based picks at Best Air Purifier UK.
FAQ
Are all ionisers dangerous? Not all emit meaningful ozone, but ionisers relocate rather than remove particles and offer less benefit than filtration. If you use one, choose an ozone-free / CARB-compliant model.
Is a small amount of ozone fine? There's no clear safe benefit to adding ozone to indoor air you breathe; the sensible approach is to avoid intentional ozone generation in occupied rooms.