A buyer named Figueroa said he paid several hundred dollars for a Sharper Image Ionic Breeze, to help remove dust, pollen and other particles from the air.1,2 Consumer Reports found that even the version fitted with an ozone-reducing attachment still adds ozone to a room, and does a poor job of removing smoke, dust and pollen.2
Ozone is a gas the US Environmental Protection Agency (EPA) calls a lung irritant: breathing it can harm your health.3 And in experiments the EPA cites, ionizers, which send charged ions into the air instead of trapping dust, were less effective at removing dust, pollen and smoke than high-efficiency particle filters.3,4 So the purifier that does the job is the plain one: a fan pushing air through a dense fibre filter, judged by how fast it cleans a room, with no ionizer, which can add ozone, and no add-on modes it doesn't need.
Buyers took the retailer to court in a class action, alleging it misled customers about the effectiveness of its air purifiers.1 The company agreed to settle while denying all allegations, and under the proposed deal it would send its air purifiers to an independent laboratory to test for ozone emissions.1,2 That case is about twenty years old, but the question it raised still applies to any purifier with an ion button.
No study we found shows that these extras have made anyone ill: the concern is the gas they can add, and the cleaning they fail to do. YAN's view: a machine that runs all night in a bedroom should only take things out of the air, never add anything to it, so we choose filter-only purifiers and read 'HEPA-type' as a sales word, not a promise.
What you need to know
- Worst is a machine built to make ozone: skip anything sold as an ozone generator or promising 'activated oxygen'.
- Skip ionizer-only units too: they clean less well than a filter, and the ion is the part that can add ozone.
- A filter unit with an ion or 'plasma' mode is a step down from filter-only: if you already own one, keep that mode switched off, and when you buy, choose a model without it.
- Best is a filter-only purifier: a fan and a filter, nothing else.
- Ignore 'HEPA-type', 'HEPA-style' or 'HEPA-like' on the box, and compare the stated cleaning rate (CADR) instead.
What 'HEPA' means, and what 'HEPA-type' doesn't
A HEPA filter is a thick, pleated sheet of very fine fibres: the fan pushes room air through it, and dust, pollen and smoke particles get stuck in the fibres. Some lesser filters look just the same: the EPA's guide to home air cleaners warns that slightly lower grades look like true HEPA filters and are sometimes mistaken for them.3
That doesn't make every lesser filter useless: the same guide says mid-grade filters are likely to be nearly as effective as true HEPA filters at catching most of the particles floating around a home.3 So a mid-grade filter with its grade stated plainly is a fair choice; what to be wary of is a box that leans on a near-miss word like 'HEPA-type' instead of naming a grade.
What actually tells you a purifier works
CADR stands for clean air delivery rate: roughly, how much cleaned air the machine puts back into the room, so a higher figure clears a room faster. AHAM, an American standards development body, says CADR is a key way to compare how well different models perform.5
The EPA does not certify purifiers or recommend brands, so it will not pick one for you.3,4 That leaves the CADR on the box or product page as the most useful figure a shopper can compare. A bigger room needs a higher rate, so compare models against the size of the room you want to clean.
Why the ion button is the problem
An ionizer works differently from a filter: it spreads charged ions into the air, and the EPA notes that it does this without a collector.3 Without a collector, the machine has no part that holds on to the dust it is meant to remove, which fits the weaker cleaning results above.
Some machines go further: sold as air cleaners, they use UV light or an electrical discharge to intentionally produce ozone.3,6 The line between the two is blurred: some of these ozone machines are built with an ionizer in the same unit, and the EPA's technical guide to home air cleaners includes a caution about ozone from ionizers.4,7
When the EPA ran one of these machines at its maximum setting in a test home, ozone rose not only in that room but in the room next door.8 For all that, ozone itself cannot do a filter's job: the EPA says it does not remove dust and pollen, the particles behind most allergies.4
California's air regulator, the Air Resources Board, puts it bluntly: "These machines are insidious."8 The board says they are marketed as "a strong defense against indoor air pollution", yet they "emit ozone, the same chemical that the ARB and the U.S. EPA (U.S. Environmental Protection Agency) have been trying to eliminate from our air for decades."8
Ozone also reacts with things already in a home to form more formaldehyde, a carcinogen and irritant, and ultra-fine particles.8,9
That is why the first step costs nothing: if your purifier has an ion, ioniser, 'plasma' or ozone button, turn it off and leave it off, because the filter keeps working without it.
This investigation continues below.
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What the rules say
California has a firm rule: since 2008, all indoor air cleaners sold there, including air cleaners sold online, must be certified by CARB, the state's air regulator, to limit their ozone emissions.10 Fully-integrated in-duct devices are currently exempted from the rule, though CARB notes that some in-duct devices may create ozone at unhealthy levels.10 CARB also strongly advises against the use of ozone generators at home.10
The same regulator has said the health benefits claimed for ozone machines have never been demonstrated, and that makers often falsely claim the devices help people with asthma and allergies.8,11
What we still don't know
Most of the evidence here is nearly twenty years old, and much of it concerns machines built to make ozone on purpose rather than the ion modes on today's purifiers. In the sources we read we found no independent test comparing 'HEPA-type' filters with true HEPA, no recent measurement of ozone from the ion and 'plasma' modes on current models, and no UK or European ozone check like California's. A recent independent test showing that those modes add no measurable ozone and clean as well as a filter would change our advice on them; until then, a gap in the data is not a clean bill of health.
What to choose
Opening a window and dusting with a damp cloth are free and add nothing to the air. If your purifier's ion mode has no off switch and you would rather be cautious, you could run it in a room where nobody sleeps. That is a precaution for a gap in what is known, how much ozone these modes add on current models, not a response to any shown harm. When the machine is due for replacing anyway, you could pick one without an ion or plasma mode, or one that lets you switch it off.
When buying, look on the box or product page for two things: a stated CADR that suits your room, and no ion, plasma or ozone function in the feature list. A true HEPA filter is a good sign, but a mid-grade filter with a strong CADR does the job too, so let the cleaning rate decide. If the listing is unclear, ask the seller one question: "Does this model have an ionizer, plasma or ozone function, and can it be switched off completely?"
Don't be swayed by health-charity seals or claims that a purifier kills germs or eases asthma; an endorsement is not a test.
We prefer the plainest machine that does the job, and not only for the clean air: a filter-only unit has one part that wears out, a filter you can swap, so the machine itself can last for years. Check that replacement filters are sold separately before you buy, change them as often as the maker says, and when the machine finally dies, take it to an electrical recycling point rather than the bin.