Air-purifying plants: what the evidence really says

"These plants purify the air in your home" is one of the most repeated headlines on the internet. It's worth looking at where it came from, because the full story is more interesting than the slogan.

Where it comes from

From a 1989 NASA study that was trying to solve a very specific problem: how to clean the air in a sealed space station. They put plants in airtight laboratory chambers, injected compounds such as benzene, formaldehyde and trichloroethylene, and took measurements. The plants — or really, mostly the microorganisms in the potting mix — absorbed them.

The result was real. The problem was the extrapolation: your living room is not a sealed chamber.

What later studies say

More recent reviews that reanalyzed that data and applied it to real rooms reached a pretty blunt conclusion: matching the effect of opening a window in a standard room would take something on the order of ten plants per square meter (about one per square foot). Natural ventilation wins by a landslide.

Put another way: two plants in a studio apartment don't change the air quality in any measurable way.

The plants on the original list

They're still excellent houseplants, just not for the reason the headline gives:

• Snake plant (mother-in-law's tongue): the toughest there is. It survives everything.
• Pothos: impossible to kill, and it propagates for free.
• Peace lily: it blooms and tells you when it's thirsty.
• Areca palm and bamboo palm: green volume, forgiving.
• Ficus elastica (rubber plant): large, glossy leaves, very decorative.
• Spider plant: fills up with babies you can give away.
• Aloe vera: also useful for minor burns.

What is well documented

The effect plants have on people, not on the air:

• Lower perceived stress and better mood in spaces with greenery.
• Better concentration in workplaces with plants, across several environmental psychology studies.
• A little humidity through transpiration, which is welcome in winter with the heating on.
• Less perceived noise in large rooms with plenty of plants.

It's less spectacular than "purifies the air," and it's real. How it applies to work is in flowers and plants in the office.

Where we stand

We could sell plants by repeating the NASA headline. We'd rather sell them for what they actually do: they make the place you're in better and help you slow down. If what you want is cleaner air, the answer is ventilation and — if needed — an air purifier with a HEPA filter.