NASA Study on Air-Purifying Houseplants Debunked: Here's the Truth
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In 1989, the National Aeronautics and Space Administration (NASA) published a promising study claiming that houseplants purify indoor air. Its results suggested that certain common indoor plants, like pothos, ivy and ficus, may absorb carbon dioxide and release oxygen through photosynthesis, and provide a natural way to remove toxic volatile organic compounds (VOCs) such as benzene, formaldehyde and trichloroethylene from the air.
“VOCs are a large group of gaseous chemicals that we tend to perceive as ‘smelly,’ like dry erase markers, perfume, paint, even essential oils,” explains Jessica Guo, Assistant Professor of Climate and Biology at Harvey Mudd College in Claremont, California. VOCs might result in a sometimes-pleasing scent, but “indoor concentrations of VOCs can be many times higher than outdoors and can cause irritation and headaches,” says Guo.
The idea that a simple houseplant could “absorb” VOCs and make the air cleaner was good news, and many publications, including Good Housekeeping, used this study as a basis to recommend “the best air purifying houseplants.”
Unfortunately, more recent studies — in particular, a review from experts at Drexel University published in the journal Nature — have shown that while houseplants offer plenty of benefits, purifying the air is not one of them. (When this research came to our attention, we took down our story on this topic.)
What is wrong with the NASA study?
In the NASA study, lead author Dr. Bill Wolverton and his team “explored how plants and their associated microorganisms could reduce indoor air pollutants in controlled environments,” notes Gioia Massa, Ph.D., senior project scientist at the Plant Processing Area at Kennedy Space Center. However, the research was performed in sealed chambers —which turned out to be a less-than-ideal substitute for real-life living spaces. Compared to those sealed chambers, indoor spaces “are larger, have persistent emissions of volatile organic compounds, and higher air exchange rates,” says Massa. “These findings highlight the complexity of indoor air quality and the need for further research to fully understand the role plants can play.”
Another problem with NASA’s data had to do with the number of plants needed to achieve the effects it reported. As Bryan E. Cummings and Michael S. Waring, the authors of the Drexel study, found, you would need 10–100 plants per square meter to clear the air in the way the NASA study reported. “[Researchers] found that the natural ventilation of a building would be doing most of the work of removing indoor VOCs, rather than the plants themselves — that is, unless you have 680 plants in your 1,500 square foot home or office,” members of the American Lung Association (ALA) wrote in a 2024 blog post.
Not that clean air isn’t a legitimate concern. “Indoor air can be more polluted than outdoor air, depending on where you live, what kind of materials your home was made from, how you cook your food, how you clean, etc.,” says Sarah Kavassalis, Ph.D., assistant professor of Climate and Chemistry at Harvey Mudd College. But if you’re worried about dust, odors, pollen, or other types of air pollution in your home and/or office, it’s best to invest in an air purifier, not a potted plant.
Still, Massa respects the work of Wolverton and his team, despite its flaws. “Science continually evolves as new tools and technologies improve our understanding,” she explains. “Just as our ability to study the stars has advanced from simple telescopes to space observatories, our understanding of biological and environmental processes has deepened.”
The other benefits of indoor plants
In case you need a reminder, indoor plants have a ton of benefits, from the aesthetic to a healthy effect on mood and even productivity. Plants can help enhance your living space, for one thing — and who doesn’t feel better when their home is beautiful? (Research has found that an attractive environment really does have a positive effect on mental wellbeing.) A 2022 study published in the International Journal of Environmental Research and Public Health found that having indoor plants around helped lower participants’ blood pressure and improve cognitive function. And if you live or work in a drying environment — think an office where the air conditioning is always on full-blast, or an apartment with central heating that results in desert-like temperatures—plants can help: they release water vapor, raising humidity levels and making the air more moist.
There are also plants with medicinal properties, like iron-rich fenugreek, tummy-soothing peppermint and the gel produced by the aloe vera plant. And finally, there’s the integral part plants play in keeping us — and our planet — alive and thriving.
“There are studies that link plants to mood and even recovery from surgery, but my favorite quality of houseplants is that they remind us where we come from,” Guo says, pointing out that plants — via the process of photosynthesis, which provides humans and animals the oxygen they need to survive — are essential for life on earth. “So I find it a nice sense of reciprocity to take care of plants, indoors or outdoors.”
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