At a glance
- The claim: Houseplants remove toxins and clean indoor air
- The study: NASA 1989; tested plants in sealed chambers, not homes
- The reality: You would need hundreds of plants per room for measurable effect
- What actually works: Ventilation and HEPA air filters
- What plants do provide: Slight humidity increase; wellbeing benefits; joy
- Still worth growing: Peace lily, snake plant, pothos, spider plant, Boston fern
Where the "air purifying plants" idea comes from
In 1989, NASA researchers published a study testing whether houseplants could remove volatile organic compounds (VOCs) from sealed chambers. The study was motivated by a real problem: the airtight design of spacecraft and space stations allowed VOCs from synthetic materials to build up with no ventilation to remove them. The researchers found that several plants absorbed measurable amounts of benzene, formaldehyde, and trichloroethylene under those controlled conditions.
The findings were genuine and the research was sound. The problem arose in how the results were communicated to the public, and how the plant industry picked up on them. "NASA says plants clean the air" became one of the most repeated plant claims on the internet, attached to lists of recommended species and used to sell houseplants with health claims that the original study never made.
Why the study does not apply to your home
The NASA experiment used small sealed containers, much higher VOC concentrations than a typical home, and specific conditions that do not resemble a normal living room or office. When researchers attempted to extrapolate those results to real-world conditions, the numbers fell apart.
A 2019 review published in the Journal of Exposure Science and Environmental Epidemiology analyzed the body of plant air-purification research and concluded that you would need somewhere between 100 and 1,000 plants per 10 square meters of floor space to achieve the VOC reduction that a modest air exchange rate through ventilation provides. That is 10 to 100 plants per square meter of floor space, far beyond what anyone keeps at home.
The rate at which plants absorb VOCs through their leaves is simply too slow, and the volume of air in a real room is too large, for the effect to be meaningful. Opening a single window for a few minutes achieves more than a room full of plants.
What plants actually do for indoor air
Plants do provide some genuine environmental benefits indoors, even if air purification is not the major one:
Humidity: Plants release water vapor through their leaves (transpiration). A significant collection of plants can raise local humidity slightly, which is beneficial in very dry environments, particularly during winter heating season. This is a real effect, though a humidifier is far more efficient at achieving meaningful humidity increase.
CO2 absorption: Plants absorb carbon dioxide during photosynthesis and release oxygen. In a room with many plants and good light, this can make a small contribution to CO2 levels. The effect is real but modest; in most homes it is negligible next to ventilation.
Psychological wellbeing: This is where the research is most consistent. Multiple studies have found that the presence of plants reduces stress, improves mood, lowers blood pressure in clinical settings, and increases feelings of calm and wellbeing. The mechanism is not air chemistry but human psychology: we respond positively to greenery and living things. This benefit is genuine, meaningful, and does not require you to own hundreds of plants.
Plants most associated with air purification
These are the plants most often cited in the air-purification literature, including the original NASA study. They are worth growing for their own reasons regardless of air quality claims:
Peace lily (Spathiphyllum): Ranked highly in the NASA study for absorbing benzene, formaldehyde, and other VOCs. Also one of the best flowering houseplants for low light. Note: toxic to cats and dogs.
Snake plant (Dracaena trifasciata): One of the most studied plants for VOC absorption. Virtually indestructible, tolerates low light and neglect, and performs some photosynthesis at night. An excellent plant for bedrooms.
Pothos (Epipremnum aureum): Fast-growing, very easy, and effective at absorbing some VOCs in lab conditions. One of the best starter plants for any light condition. Note: toxic to cats and dogs.
Spider plant (Chlorophytum comosum): Easy to grow, produces many offsets, and among the plants tested for formaldehyde absorption. Non-toxic to cats and dogs, which makes it a good option for pet households.
Boston fern (Nephrolepis exaltata): High transpiration rate, which does raise humidity noticeably if you keep several. Requires more humidity and consistent moisture than the above options. Non-toxic to pets.
Rubber plant (Ficus elastica): Large leaves, tolerates medium light, and absorbs formaldehyde in lab conditions. Easy to grow once established.
The honest takeaway
Grow houseplants because they bring life and beauty to your home, because they connect you to something living, and because the psychological benefits of caring for plants are genuine and well-documented. Do not grow them primarily to improve your air quality: they will not do that in any meaningful way compared to opening a window or running an air purifier.
The good news is that the plants traditionally recommended for "air purification" are, almost without exception, excellent houseplants for completely separate reasons. Peace lily, snake plant, pothos, and spider plant are all genuinely good houseplants. You just do not need to justify them with health claims.