Walk into any plant shop and you will probably see a label promising that a snake plant or peace lily will "purify your air." The idea is everywhere, from home decor blogs to gift guides, and it usually traces back to a famous NASA study.
Walk into any plant shop and you will probably see a label promising that a snake plant or peace lily will "purify your air." The idea is everywhere, from home decor blogs to gift guides, and it usually traces back to a famous NASA study. It is a lovely thought: buy a few plants and breathe easier.
The reality is more interesting. Plants are wonderful for a home, but the research on air cleaning tells a different story than the labels.
Where the idea came from
The claim has its roots in research led by NASA scientist B. C. Wolverton in the 1980s. His team studied whether plants could help remove chemicals from the air in sealed spaces, a question that mattered for long term spaceflight. A widely cited 1989 report, "Interior Landscape Plants for Indoor Air Pollution Abatement," described plants removing certain volatile organic compounds from small sealed test chambers.
Those findings were real, but the conditions were very different from a home. The chambers were small and sealed, and the experiments ran for many hours or days. A typical house is far larger and constantly exchanges air with the outdoors.
What a 2019 review found
In 2019, two researchers at Drexel University, Bryan Cummings and Michael Waring, published a review in the Journal of Exposure Science and Environmental Epidemiology with a blunt title: "Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies."
They looked at 12 published chamber studies and translated 196 experimental results into a standard metric used for air cleaners, the clean air delivery rate, or CADR. This let them compare plants with the way real buildings already refresh their air.
Their findings:
- Single plant clean air delivery rates varied enormously, by orders of magnitude.
- The median was about 0.023 cubic meters per hour, which is very small.
- To match the removal that ordinary outdoor to indoor air exchange already provides in a typical building, you would need somewhere between 10 and 1,000 plants per square meter of floor space.
Put another way, for a living room of about 20 square meters, you would need at least 200 plants, and possibly many thousands, to make a measurable difference to VOC levels. That is a jungle, not a decor accent.
The authors suggested future research focus on other questions, such as how plants take up VOCs, other biofiltration technologies and the well being benefits of plants, as well as possible emissions from plants and potting soil.
Why indoor air still matters
None of this means indoor air quality is unimportant. The U.S. Environmental Protection Agency says that levels of several organic pollutants average 2 to 5 times higher indoors than outdoors. Common sources include paints, cleaning products, air fresheners, glues, some building materials and furnishings, and stored fuels.
The EPA also notes that during and for several hours after activities such as paint stripping, levels can be far higher than outdoor background levels. That is why the agency emphasizes ventilation and source control.
What actually improves indoor air
If you want cleaner indoor air, the EPA's general advice points to a few steps that do far more than plants.
Reduce sources. Choose products with fewer harsh chemicals, follow label directions and avoid storing opened paints, solvents and similar products indoors. Buy in quantities you will use soon.
Ventilate. Open windows when weather allows, especially while painting, cleaning or cooking. Use bathroom and kitchen exhaust fans that vent outdoors.
Follow product labels. The EPA notes that potentially hazardous products often carry warnings to reduce exposure, such as using them in a well ventilated area.
Never mix household products unless the label tells you to.
Consider an air cleaner if you need one. Portable air cleaners are rated by clean air delivery rate, the same metric the 2019 review used. If you have a specific concern, such as wildfire smoke or allergies, a properly sized cleaner will do much more than any number of plants.
If you are planning a paint project, our article on low VOC paint labels covers how to choose and ventilate.
So why keep houseplants?
Plenty of reasons. Plants bring color, texture and life to a room. They soften hard lines, add height to a corner and connect an indoor space to the outdoors. Caring for them can be a calming routine. Plenty of people simply feel better in a room with greenery, and the Cummings and Waring review itself pointed to well being as a more promising area to study than air cleaning.
That is the heart of biophilic design: bringing natural elements indoors because they make spaces feel better to live in.
Choosing plants for the right reasons
If you are buying plants for beauty and mood rather than air cleaning, choose them for your light and lifestyle:
- Low light rooms: look for plants known to tolerate lower light, and accept slower growth.
- Bright windows: many trailing and leafy plants thrive near a bright window without harsh direct sun.
- Busy schedules: choose forgiving plants that tolerate missed waterings.
- Homes with pets: check whether a plant is safe for cats and dogs before you bring it home, since some common houseplants are toxic to pets.
A few healthy plants placed where you will see and enjoy them every day will do more for your home than a crowd of struggling ones.
A note on overwatering
Overwatered plants and soggy soil can encourage mold growth, which is the opposite of what you want for indoor air. Let the top of the soil dry out between waterings for most common houseplants, and make sure pots drain properly.
The takeaway
The famous NASA research showed plants can remove some chemicals in small sealed chambers. But a 2019 review of the evidence concluded that potted plants do not meaningfully improve indoor air in real homes, because ordinary ventilation already moves far more air than any realistic number of plants can clean. For better air, reduce sources and ventilate. For a better home, keep the plants anyway. They just need to be enjoyed for what they really do.
Sources
- Cummings BE, Waring MS. Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies. Journal of Exposure Science and Environmental Epidemiology. 2020;30:253 to 261. https://doi.org/10.1038/s41370-019-0175-9
- Europe PMC record and abstract (PMID 31695112). https://europepmc.org/article/MED/31695112
- U.S. Environmental Protection Agency. Volatile Organic Compounds' Impact on Indoor Air Quality. https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality
- Wolverton BC, Johnson A, Bounds K. Interior Landscape Plants for Indoor Air Pollution Abatement. NASA Technical Memorandum 101766; September 15, 1989. https://ntrs.nasa.gov/citations/19930073077
