Do Indoor Plants Actually Improve Air Quality? Scientists Weigh In

Image by Tim Newman / iStock

Ah, indoor plants. We love them, we care for them, and we become borderline grief-stricken when we accidentally kill them.

There are many benefits to having greenery in your bedroom or office space, including fulfilling the need for companionship, reducing stress and anxiety, and promoting faster healing. Another pro of plants? According to a clean air study run by NASA in 1989, certain houseplants can remove toxic agents (like benzene, formaldehyde, and trichloroethylene, to name a few infamous pollutants) from the air.

However, a new review published in the Journal of Exposure Science and Environmental Epidemiology says that we may be overestimating the air-purifying benefits of houseplants. It found that traditional ventilation systems in homes and buildings (such as air conditioning systems or, you know, a couple of open windows) actually clean the air much faster than potted plants can.

What exactly did the new study find?

During the study, Drexel College of Engineering professor Michael Waring, Ph.D., and his student, Bryan Cummings, analyzed over a dozen studies on plants' air-purifying properties that spanned 30 years of research. They found that NASA's 1989 clean air study claim that plants could remove air pollutants wasn't entirely true.

That's because the study (and others that followed) was conducted in a sealed chamber lab rather than a home or office building, and the results weren't analyzed further to determine whether plants would have the same effects in a realistic indoor environment. While NASA's results might have been profound for cleaning the sterile air in space stations, it looks like the general public took this information and ran right to the plant store.

"Typical for these studies," the researchers say, "a potted plant was placed in a sealed chamber (often with a volume of a cubic meter or smaller), into which a single volatile organic compound (VOC) was injected, and its decay was tracked over the course of many hours or days."

To further examine their findings, the two researchers created a measure they named a "clean air delivery rate” (CADR). When they dove back into 30 years of plant studies, they used this CADR framework to calculate the rate at which plants would dilute VOCs in the air. In nearly all of the studies, the plants' CADR was actually way slower than traditional methods of air exchange in buildings.

But before you berate your houseplants for not doing their job, Waring and Cummings acknowledge that many of these controlled plant studies did show a reduction in VOCs over time—it was just a very, very long time. They concluded it would take between 10 and 1,000 plants per square meter of floor space to purify the air at the same pace as an air conditioning system. 

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Here's what it means for our potted plant obsession.

Waring sees this review as a sign that scientists should take the opportunity to reanalyze any bold claims that have previously been made in their fields. "This is certainly an example of how scientific findings can be misleading or misinterpreted over time," he says. "But it's also a great example of how scientific research should continually reexamine and question findings to get closer to the ground truth of understanding what's actually happening around us." 

Although your plants might not actually be purifying the air in your home, we shouldn't forget about the host of other benefits they have for our well-being. Plus, they offer a nice scent and cozy feel to your space. Rest assured that we at mbg will remain the most passionate of plant people.

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