The dozen air-purifying plants you have overwhelming your living room might not be doing the job you hoped. Here's the science behind it.
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Between your 9-to-5 desk job, the hour or so you spend pumping iron at a stuffy gym, and all your late-night Netflix binges, it's no surprise that you probably spend about 90 percent of your time indoors. Factor in the coronavirus outbreak and the subsequent stay-at-home orders, and the last time you ventured out into the outdoor world—even if it was just to walk to the grocery store—might have been three days ago. 

With all that extra time you've been spending in your humble abode, you might have gathered the motivation to transform it into a healthy living space, starting with buying air-purifying plants. After all, the concentrations of some pollutants can be two to five times higher indoors than they are outside, thanks to cleaning supplies, paint, and the construction material used in your building, according to the Environmental Protection Agency. And these volatile organic compounds (VOCs, aka the gasses emitted from these household products and more) can lead to harmful health effects, including eye, nose, and throat irritation; headaches and nausea; and liver damage, among others, per the EPA.

But is that parlor palm sitting on your windowsill or snake plant on the end table next to your couch doing anything to help the situation?

Sadly, even if your home looks like it belongs on Instagram's Discover page, it's not going to have air that's as pure as oxygen straight out of a tank. "The most common misconception is that plants clean the air—they don't," says Michael Dixon, director of the Controlled Environment Systems Research Facility at the University of Guelph in southern Ontario, Canada. "Houseplants play an extremely small role in the atmosphere quality of the space that they're in, and their impact is probably far greater in that their aesthetic quality just makes you feel good."

In fact, a 2019 review of 12 published studies on potted plants' effect on airborne VOCs discovered just that. Published in the Journal of Exposure Science and Environmental Epidemiology, the review found that air exchange, either by opening up windows or using ventilation systems, reduces concentrations of VOCs much faster than plants can extract them from the air. That means you'd need anywhere from 100 to 1,000 plants per square meter (roughly 10 square feet) of floor space to remove VOCs as effectively as cracking open your living room windows. If you want to actually live in your house, that's not exactly feasible.

Behind the Myth

So how did the misconception that a few potted plants would turn your home into a fresh-aired oasis gain traction? It all started back in the late-1980s with NASA scientist Bill Wolverton, says Dixon, who co-authored a 2011 study on the subject published in Comprehensive Biotechnology. In order to find out which plants did the best job filtering various pollutants, Wolverton tested a dozen common houseplants—such as the gerbera daisy and the bamboo palm—in their ability to remove household toxins from a 30-inch by 30-inch sealed chamber, according to NASA. After 24 hours, Wolverton found that the plants successfully removed 10 to 90 percent of the contaminants, including formaldehyde, benzene, and trichloroethylene, in the air. (Related: Air Quality Affects Your Workout [and Your Health] More Than You Think)

The problem with the research: Wolverton subjected the plants to doses of pollutants 10 to 100 times greater than you'd typically find in poor-quality indoor air, and they were placed in very small chambers, says Dixon. In order to get the same effects, Wolverton calculated that you'd need to have about 70 spider plants in a modern, energy-efficient 1800-square-foot home. Translation: The results wouldn't necessarily apply to a real-world set-up like your mid-sized condo.

In some cases, your Plant Mom status could even be making your air quality worse. The potting soil can be a source of contaminants in the atmosphere, especially if you over water or use too much fertilizer, says Dixon. Overly damp soil can promote the growth of microorganisms that can spark allergies in some people, and the salts from excessive fertilizer use can evaporate into the air, he adds.

Do Air-Purifying Plants Have *Any* Effect?

Think back to your high school biology class, and you'll have a pretty solid understanding of what your air-purifying plants can *actually* do: Take in carbon dioxide and give off oxygen through photosynthesis, says Dixon. Houseplants innately have metabolic pathways (the chemical reactions in cells that build and break down molecules for cellular processes) to use up carbon dioxide, but they don't have enough of the ones that take in the hazardous contaminants found in poor-quality air to make a significant impact, he explains. (At least maintaining an indoor garden will give you fresh produce too.)

Even then, houseplants aren't air-cleaning, CO2-busting machines. Since most indoor spaces have low light levels, plants typically function at the point when the rate of respiration (taking in carbon dioxide and releasing oxygen and some CO2) is equal to that of photosynthesis, says Dixon. At this point, a plant is taking in the same amount of CO2 from the air as it is producing it. As a result, "the prospect of potted plants being a major player in enhancing the atmosphere quality of an indoor space is very small," he explains.

But the air-purifying qualities of some plants aren't a total hoax. In some very specific conditions, the VOCs can act as food for the communities of microbes (re: bacteria and fungi) in the plant's root zone, creating a "biofilter" that reduces contaminants in the air. However, this isn't something you can achieve with your pothos plant, says Dixon. For starters, these biofilters of plants are designed to cover entire walls and span three to four stories high.

These enormous, plant-filled walls are porous and have water circulating through them to create the optimal environment for the microbes to happily live, known as the biofilm. Fans in the system pull the room's air through the soil, and any VOCs dissolve into the biofilm, says Dixon. When the plants perform photosynthesis and leak carbohydrates out to the roots, the microbial communities living in the biofilm munch away on it—along with any contaminants that were sucked into it, he explains. "The volatile organics that we associate with poor-quality indoor air are sort of a snack [for the microbes]," says Dixon. "The [VOCs] aren't in high enough concentration to fully sustain a microbial population—so the plants do that [through photosynthesis]." 

Attempting to DIY your own biofilter in a potted plant is "very, very difficult," due to those low light levels found in homes, says Dixon. Not to mention, they're super complex to maintain and not available for home use yet. But you're not totally SOL if you want to cleanse your indoor air: "Literally, just open the window, which will enhance the gas exchange with the outdoors," he says.  (And if your home is way too muggy, turn on one of these top-rated dehumidifiers.)

And while your air-purifying plant may not do the job you hoped it would, at least being around the greenery could help you be more productive and reduce your stress levels, according to the research from Washington State University. Plus, taking care of them is good #adulting practice before you finally adopt a puppy, right?