Journal/Plant Science & Curiosities · 5 min read
Do Plants Really Clean Indoor Air? What NASA Actually Found
The famous 1989 NASA Clean Air Study is quoted everywhere — and misunderstood everywhere. Here's what the research actually shows.
Quick answer
The 1989 NASA study did show houseplants remove volatile organic compounds (VOCs) — but in sealed 0.9 m³ chambers, not real rooms. Later research shows you'd need roughly 100–1,000 plants per average room to match a single open window. Plants have real benefits, but air purification isn't the main one.
Search 'houseplants that clean air' and you'll find a hundred articles citing the NASA Clean Air Study. Almost none of them mention what NASA actually did or how the results scale up. The truth is more nuanced — and more interesting.
What NASA actually tested
In 1989, NASA researcher B.C. Wolverton tested 12 common houseplants inside sealed 0.88-cubic-metre acrylic chambers. He injected known concentrations of benzene, trichloroethylene, and formaldehyde and measured how quickly the plants' leaves and soil microbes broke them down. Result: they did, meaningfully, in a sealed box.
Where it falls apart in a real room
A 2019 systematic review by Cummings and Waring (Drexel University) crunched 30 years of follow-up studies. The finding: real rooms exchange air with outdoor air constantly — typically once every 1–2 hours. That exchange dilutes VOCs faster than any realistic number of plants can absorb them. To match a single open window in a 30 m² room, you'd need somewhere between 100 and 1,000 plants.
So plants don't help at all?
They do, just marginally. Under sealed conditions (an unventilated bedroom overnight), a handful of plants can measurably reduce specific VOCs. In real, ventilated homes, the effect on air quality is small compared to opening a window, using a HEPA filter, or reducing the source.
What plants DO help with indoors
- Humidity — a shelf of leafy plants raises local humidity by 5–15%, real and useful in winter.
- CO₂ during the day — plants absorb CO₂ and release oxygen. Effect is small but present.
- Particulate dust — some plant leaves catch fine dust, wiping them off does clean the air.
- Psychological wellbeing — the strongest, most consistent effect of all.
If you actually want cleaner indoor air
- Ventilate — open windows for 10 minutes twice a day.
- Reduce VOC sources — off-gassing paint, cleaning products, air fresheners.
- Use a HEPA + activated carbon filter for real particulate and VOC removal.
- Add plants for the humidity and mood benefits — think of them as bonus, not filter.
PlantMe recommends plants for the environment and space you have — including which perform slightly better as passive humidifiers.
Frequently asked questions
Which plant cleans air best?
Under NASA's sealed conditions, peace lily and areca palm had among the highest removal rates. In real rooms the differences are academic — ventilation wins by orders of magnitude.
Do plants release CO₂ at night?
Yes, all plants do (respiration). The amount is small — a bedroom-full of plants releases roughly the same CO₂ overnight as one adult breathing. Not a health concern.
Are there any plants I shouldn't put in a bedroom for air-quality reasons?
No — the CO₂ effect is negligible. Choose based on humidity, allergies (some plants shed pollen), and pet safety instead.
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