What are ionizer air purifiers and ionizers in general? This is an important question because ionizer air purifiers are all over the place.

For example, I was at a friend’s apartment in the US, and I saw his tower fan air purifier had an ionizer button on it:

Ionizer air purifiers are often marketed with a variety of names, such as “ion air purifiers”, “negative ion air purifiers”, “air ionizers,” and “bipolar needlepoint ionization”. Let’s cut through the marketing hype and find out what they are and whether they work or not. It’s also important because several friends in China have sent me links to ionizer air purifier products like this:

Amazing! A “miraculous ionizer air purifier” that removes PM2.5 and formaldehyde in just 30 seconds. And all that for far cheaper than regular purifiers and even cheaper than building your own purifier.

So do popular ionizer air purifiers such as the Ionic Pro air purifier and Clarifion air purifier work?

So How Do Air Ionizer Purifiers Work?

Here’s how air ionizers work. Let’s say I have an ionizer air purifier, and some bad particles are floating in the air.

That air ionizer shoots out negative ions into the air.

Those negative ions in the air cause the particles to stick to surfaces, like my bed, the wall, and the floor.

That’s the principle behind air purifiers with ionizers. It’s hard to see it happening with these tiny negative ions, but you’ve seen it on a visible scale if you’ve seen someone rub a balloon on their hair and then stick it to a wall.

Why Air Purifier Companies Use Ionizers in Purifiers

Most of the major air purifier companies use ionizers in their air purifiers, including Xiaomi, Blueair, Levoit, and many more. The reason is simple: a cheap ionizer can slightly improve the efficiency of the HEPA filter. This way, air purifier companies with little added costs can market a higher CADR (metric measuring the effectiveness of air purifiers), making it a cheap way to get a boost in CADR. Unfortunately, much of the time the user is unaware an ionizer is being used and unaware of the possible harmful effects.

Why Ionizer Air Purifiers Are Not Recommended

But wait #1 – Ionizers Are Too Weak

A summary of scientific tests of air purifiers found that most air ionizers have no noticeable effect on particulate levels (p. 8). They conclude that most ionizers are too weak to have an effect. Studies do show an effect if they use very strong ionizers–much stronger than most ionizers on the market (p. 19).

But wait #2 – Ionizers Produce Harmful Ozone

OK, so regular ionizers don’t work, but we can use a strong one! The problem is that when you put that many ions into the air, it produces ozone. Ozone is harmful, so that’s not good!

Read More: Blueair Air Purifiers Review: Ionizer and Ozone a Health Danger?

But wait #3 – Ionizers Can Create Harmful Particulate Matter (PM2.5)

Ionizers have been shown to increase dangerous small particulate levels by over 8x. This is due to chemical reactions the ionizer helps create in the air.

Read More: Study Finds Ionizers Increase Air Pollution

But wait #4 – Ionizers Create Harmful VOC Gases

Ionizers can create a variety of VOCs, including those produced by the Global Plasma Solutions bipolar ionizer in schools: acetone, ethanol, toluene, butyraldehyde, and acetaldehyde. Furthermore, an academic research study found that ionizers can actually create formaldehyde.

Read More: Air Ionizers Worse Than Diesel Exhaust

But wait #5 – Ionizers Make Things Dirty

Even if we use a really strong ionizer and even if we can accept the ozone, you might have noticed that the ionizer didn’t actually filter out the particles. It just made them stick to my bed, wall, and floor.

First, that’s gross. Since the particles floating around in cities like Beijing, Delhi, and Los Angeles include things like arsenic cadmium, and lead, I’d rather not have them stick to my pillow.

Second, they’re still a danger. The particles are just sticking to my bed. So let’s say Thomas comes home:

When I sit down on my bed, I’ll dislodge those particles, and they’ll float back into the air. Here’s my super scientific rendering of that process:

Those problems are what led Consumer Reports to publish tests and warn people not to buy the Sharper Image Ionic Breeze. Sharper Image sued Consumer Reports; Consumer Reports won.

So when people send me links asking about these “miraculous” ionizer purifiers, I tell them to steer clear. Unfortunately, even as the word is getting around that ionizers cause more harm than good, school districts and airports around the United States have been tricked into shelling out millions of companies pitching these harmful products.

One Big Reason Why Ionizers Are Unnecessary

In my mind, the biggest reason ionizers are unnecessary is that there’s already technology out there that is low-cost and highly effective. I use HEPA filters. HEPAs actually capture particles–be it PM2.5 or PM10–and they are backed by empirical tests (1, 2, 3, 4, 5, 6).

Read More: 4 Steps to Choosing the Best HEPA Air Purifier

Not convinced about the effectiveness of air purifiers? You can see the effectiveness of HEPA filters in action in this live test I did of a HEPA filter chewing through real Beijing air:

Smart Air Original DIY Air Purifier Live Test with Dylos Particle Counter (CN Subtitles)

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What’s more, HEPA filters don’t create other harmful pollutants like ozone. So I steer clear of ionizer air purifiers. If your fan or HEPA purifier has an ionizer mode on it, I recommend keeping it switched off.