What is ozone?
In one line: ozone (O₃) is a highly reactive form of oxygen. High in the atmosphere it protects us, but at ground level and indoors it's a lung irritant. Some "ozone generators" and certain ionisers produce it deliberately or as a by-product — which is why we recommend sealed HEPA+carbon filtration instead.
What it is
Ozone is a molecule of three oxygen atoms (O₃) rather than the two in the oxygen we breathe (O₂). That extra atom makes it unstable and reactive — it readily attacks other molecules, which is why it can break down some odours and is used in industrial settings. The same reactivity is what makes it harmful to breathe: it reacts with the delicate tissue in your airways and lungs.
Why it's a concern indoors
Breathing ozone can cause throat irritation, coughing, chest tightness and shortness of breath, and it can worsen asthma and other respiratory conditions. Health authorities do not recommend ozone-generating air cleaners for occupied spaces, because reaching levels high enough to "clean" the air also means levels high enough to irritate the people in it. Ozone can also react with other indoor chemicals to form additional irritating by-products.
Where it comes from in "air purifiers"
- Ozone generators — devices that intentionally emit ozone, sometimes sold for odour or "sanitising." Not for occupied rooms.
- Some ionisers / "plasma" units — can emit ozone as a by-product (more here).
- Some UV and PCO units — depending on design (UV-C air purifiers).
Plain HEPA + activated-carbon filters produce no ozone — they physically trap particles and adsorb gases. That's the safe route.
Next step
Want ozone-free filtration you can trust? Browse the CleanAirKits store, and see can air purifiers make you sick?
FAQ
Is ozone dangerous to breathe? Yes at indoor-relevant levels — it irritates the airways and can worsen asthma. Ozone-generating cleaners aren't advised for occupied rooms.
Do HEPA air purifiers produce ozone? No — HEPA and carbon filters trap and adsorb without generating ozone. Only ionising/ozone/some UV designs can.