Do Houseplants Improve Indoor Air Quality? We Asked an Environmental Scientist

It’s one of those things that we’ve all absorbed for so long we just accept it as truth: Plants are good for our indoor air quality. You’ve heard it countless times, right? Maybe even said it yourself when you’re buying yet another ZZ plant (... or maybe that's just us!).

But hey, we can’t be faulted. This tidbit of conventional wisdom is so ingrained in our collective conscience, why would we doubt it? Well, as it turns out, science. We went to a leading expert on the topic (an environmental scientist!) to settle whether or not your beloved houseplants really do improve indoor air quality.

Do Plants Improve Air Quality?

The short answer (sorry!) is no. A 2020 review and analysis of decades of research on volatile organic compound (VOC) removal efficiencies (aka cleaning air of pollutants), concluded for the Journal of Exposure Science & Environmental Epidemiology that in no uncertain terms: Potted plants do not improve indoor air quality.

In fact, Richard L. Corsi, PhD, dean of the College of Engineering at University of California, Davis, didn’t mince words, answering our questions as he was headed to Honolulu for Indoor Air 2024, the largest gathering of indoor air quality researchers from around the world. “Of the nearly 1,000 participants,” he says “not one is speaking about plants removing indoor pollutants. We know it makes no sense at all.”

Why, though? According to Dr. Corsi, VOC reduction levels “that are even perceptively measurable in a small home would require approximately 500 to 1,000 house plants.” 

Not ready to give up believing in your Monstera? “I could hang old pairs of socks or T-shirts and get similar results,” said Dr. Corsi. But what if we’re tempted to just pack the house with all things green? ”Even if the house is made into a jungle to remove small amounts of pollutants, there would be a lot of watering and likely humidity issues.”  he cautions.

If we really want to improve air quality, “there are a lot of actual technologies, particularly media filtration for particles and activated carbon or zeolites for VOCs and (if done right) for ozone and nitrogen dioxide,” he says.  

Why Do We Believe Plants Clean the Air?

So how is it that we all came to believe in something that is so patently untrue? It turns out the original culprit may have actually been NASA. Yes, back in 1989, NASA conducted A Study of Interior Landscape Plants for Indoor Air Pollution Abatement. And their results showed “that plants can play a major role in removal of organic chemicals from indoor air.” 

Here’s the caveat: Their testing was done in a controlled environment, a closed chamber. They tested individual VOCs in these laboratory settings and did find a decrease in the pollutants over time. But a small, sealed chamber definitely doesn’t mimic a typical home in the real world, where we also have more than one single pollutant at a time! And according to the American Lung Association, somewhere in the order of 10 to 1,000 plants per square meter would be required to achieve the same level of results that studies like this have found. 

And there’s more: Besides the size difference in lab settings and actual homes, we also have doors and windows frequently opening and closing, plus infiltration happening all over the place, bringing in a constant supply of new air and removing the old. The American Lung Association has also reported that “few studies have looked at the impact of plants within a natural, indoor environment. Those that do exist have faced challenges, including inaccurate measuring equipment and failure to control or measure the air exchange rate.”

In short, studies conducted in unrealistic environments can’t be applied to our homes. It would take more plants than would be feasible for anyone to maintain to achieve any kind of discernible air quality improvement. “Plants are nice. I like them,” says Dr. Corsi. “I have two in my office and several at home. They look nice, but I know they do nothing to improve my [indoor air quality].” 

But hey, chances are you love your plants for many reasons beyond just hoping they make your indoor air better. And if they make you happy, isn’t that what counts?