What the Famous NASA Study Found
Back in 1989, NASA published its Clean Air Study to explore ways to clean the air in sealed environments like space stations. Researchers placed common houseplants inside small, sealed chambers and pumped in specific volatile organic compounds (VOCs)—nasty
chemicals like formaldehyde, benzene, and trichloroethylene, which can be found in everyday items like furniture, paint, and cleaning supplies. The results were promising: they found that certain plants could absorb these pollutants from the air, removing a significant percentage over a 24-hour period. The study identified a process called phytoremediation, where plants and the microorganisms in their soil metabolise these toxins.
The Superstar Air-Cleaning Plants
The study identified several plants as being particularly effective. While all plants tested showed some ability to remove pollutants, a few stood out. The Peace Lily (Spathiphyllum) was a star performer, shown to remove all three major VOCs tested initially, plus others like ammonia in later research. Other top contenders included the Snake Plant (Sansevieria), also known as Mother-in-Law's Tongue, which is famously resilient and great at filtering formaldehyde. The list also featured the Spider Plant (Chlorophytum comosum), English Ivy (Hedera helix), and various types of Dracaena. These plants became household names for anyone looking to create a healthier indoor environment, and their popularity has endured for decades.
The Reality Check: The Catch in the Context
Here’s the part that often gets lost in translation. The NASA experiments were conducted in small, airtight chambers, which are nothing like a typical home or office. Your house has natural ventilation—air moving through windows, doors, cracks, and HVAC systems. This air exchange naturally dilutes and removes pollutants far more effectively than a few potted plants can. Later analysis of the NASA data revealed a staggering reality: to achieve the same air-cleaning effect in an average-sized room, you would need an impractically large number of plants. One review estimated it would take anywhere from 10 to 1,000 plants per square meter of floor space to make a meaningful difference. So, unless you plan on living in a dense jungle, your four or five houseplants are having a negligible impact on air quality.
So, Do Plants Purify Air at All?
Technically, yes, but not in a way that matters for your health in a real-world setting. The rate at which plants remove VOCs is much, much slower than the rate at which new air enters your home. Think of it like trying to empty a bathtub with a teaspoon while the tap is still running. The effect is there, but it’s too small to count. Modern science communicators and even the American Lung Association now state that houseplants are not an effective way to purify indoor air. The original study was groundbreaking for its controlled environment but has been widely misinterpreted for everyday applications. For clean air, you’re better off focusing on ventilation and reducing sources of pollution in the first place.
The Real, Proven Benefits of Houseplants
Just because they aren't miracle air purifiers doesn't mean you should give up on your green friends. The true benefits of keeping plants indoors are primarily psychological, and they are significant. Studies have consistently shown that interacting with indoor plants can reduce stress by lowering cortisol levels. They can also improve mood, enhance concentration, and boost productivity, which is why they are so popular in office environments. There's also the simple aesthetic pleasure and the connection to nature, known as biophilia, that tending to a living thing provides. This boost to mental well-being is a powerful reason to cultivate an indoor garden.
