The Origin of the Claim
The belief that houseplants are tiny, green air purifiers stems from a landmark 1989 NASA study. Researchers, looking for ways to clean the air in sealed environments like space stations, placed common houseplants in small, airtight chambers. They then
injected volatile organic compounds (VOCs)—like formaldehyde and benzene, which are common indoor pollutants from furniture, paints, and cleaning supplies—into these chambers. Over 24 hours, they observed that plants like the peace lily and English ivy were indeed capable of removing a significant percentage of these chemicals from the sealed air. The study was a success within its specific context and sparked a decades-long trend of promoting plants for their 'air-purifying' abilities.
The Lab vs. Your Living Room
The catch, however, lies in the vast difference between a small, sealed lab chamber and a typical room in a house. Your home is not an airtight container. Air constantly flows in and out through windows, doors, and ventilation systems. This process, known as air exchange, dilutes and removes pollutants far more quickly and effectively than a few plants can absorb them. A 2019 review of dozens of studies concluded that while plants do remove VOCs, the rate is so slow in a real-world setting that it's negligible compared to a building's natural ventilation. The air in your room is likely to be replaced by outdoor air long before your spider plant has had a chance to make a dent in the pollutant levels.
It's a Numbers Game
To replicate the air-cleaning effects seen in the NASA study, the sheer number of plants required is staggering. Researchers have calculated that you would need anywhere from 10 to 1,000 plants per square meter of floor space to compete with a building's standard air exchange rate. For a small 150-square-foot room, this could mean housing several hundred to over a thousand plants, essentially turning your living space into a dense jungle. One analysis found that a standard HEPA air purifier cleans the air of particles thousands of times faster than a single houseplant can remove gases. So, while plants technically do clean the air, you would need an impractical number to achieve a 'meaningful' result.
The Real, Proven Benefits of Plants
This doesn't mean you should give up on being a plant parent. While their air-purifying skills may be overstated, the other benefits of having indoor plants are well documented and significant. Studies have consistently shown that being around plants can reduce stress, improve mood, and increase feelings of well being. Tending to plants connects us with nature, an idea known as biophilia, which has proven psychological benefits. They add humidity to dry indoor air through transpiration, which can be helpful during winter months. And, of course, they add beauty, colour, and life to our homes. These aesthetic and psychological boosts are powerful reasons to fill your space with greenery.
