What is an air purifier?
In one line: an air purifier is a device that draws in room air, passes it through one or more filters to remove airborne pollutants — mostly fine particles, and (with activated carbon) gases and odours — and returns cleaner air to the room.
The basic idea
At its simplest, an air purifier is a fan plus filters in a box. The fan pulls air in; the filters trap what you don't want to breathe; the cleaned air comes back out. Repeat that fast enough and the whole room's air is cleaned several times an hour. What it removes depends on the filters: a HEPA or MERV-13 filter captures particles like dust, pollen, pet dander and smoke (PM2.5); an activated carbon stage handles gases and smells. See how an air purifier works for the full path.
What it's for
People use air purifiers to reduce allergens (pollen, dust mites, pet dander), clear smoke and cooking particles, lower indoor pollution that drifts in from outside, and cut airborne virus-carrying particles. The key number is clean-air delivery rate (CADR) — how much clean air it actually delivers — matched to your room size.
What it is not
- Not a humidity control. It doesn't add or remove moisture — that's a humidifier or dehumidifier.
- Not a ventilator. It recirculates and filters indoor air; it doesn't lower CO2 or bring in fresh air — see air purifier vs opening a window.
- Not a medical device — it can reduce airborne triggers, but it doesn't treat conditions.
Next step
New to this? Read do air purifiers work? and what size you need, or see picks at Best Air Purifier UK.
FAQ
Is an air purifier the same as an air filter? An air filter is the component; an air purifier is the whole device (fan + filters + housing) that moves air through the filter.
Do all air purifiers use filters? Most do. Some use ionisers or UV instead or as well — see ionisers & ozone and UV-C; a mechanical filter is the most reliable, best-evidenced approach.