The 1989 NASA Clean Air Study
In 1989, NASA, in association with the Associated Landscape Contractors of America, published a study titled "Interior Landscape Plants for Indoor Air Pollution Abatement." The goal was to determine if common houseplants could help clean the air in sealed
environments, like a space station. The researchers placed a variety of plants inside small, sealed plexiglass chambers and injected common volatile organic compounds (VOCs) like formaldehyde, benzene, and trichloroethylene—chemicals often found in building materials, furniture, and cleaning products. The results were promising: over 24 hours, certain plants removed a significant percentage of these pollutants from the air within the chamber. This study became the foundation for the widespread belief in air-purifying houseplants.
The Snake Plant (Dracaena trifasciata)
Often hailed as one of the hardiest and most low-maintenance houseplants, the Snake Plant was a star performer in the NASA study. It was noted for its ability to filter formaldehyde, a common indoor pollutant found in cleaning products, tissues, and personal care items. What makes the Snake Plant particularly interesting is its ability to perform photosynthesis using the crassulacean acid metabolism (CAM) process. This means it can open its stomata at night to take in carbon dioxide and release oxygen, unlike most plants that do so during the day. While this has led to the popular belief that it's the perfect bedroom plant for round-the-clock air refreshment, the actual volume of oxygen produced is quite small.
The Peace Lily (Spathiphyllum)
The elegant Peace Lily, with its glossy dark leaves and white spathes, was found to be effective at removing several toxins. NASA's research highlighted its ability to filter benzene, formaldehyde, trichloroethylene, xylene, and ammonia from the air. Benzene is a widespread pollutant found in plastics, resins, and synthetic fibres, while ammonia is a component of many window cleaners and fertilizers. The Peace Lily is a relatively easy plant to care for, known for its helpful habit of drooping slightly when it needs water, taking the guesswork out of its maintenance schedule. Its ability to thrive in lower light conditions also makes it a versatile choice for many homes.
The Spider Plant (Chlorophytum comosum)
The resilient and fast-growing Spider Plant is another popular choice for novice plant owners. It's easily recognizable by its arching leaves and the spider-like plantlets, or "pups," that dangle from the mother plant. In the NASA study, it was a champion at removing formaldehyde from the air. Due to its non-toxic nature for pets and children and its adaptable care requirements, the Spider Plant has remained a household favourite for generations. Its reputation as an air purifier only adds to its long-standing appeal as a decorative and functional piece of greenery for any indoor space.
From Sealed Lab to Ventilated Living Room
Herein lies the crucial context often missing from the conversation. The NASA experiments were conducted in small, sealed chambers—a controlled environment vastly different from a typical home or office. Our homes have much larger volumes of air and are constantly subject to ventilation, whether from open windows, doors, or HVAC systems. This air exchange dramatically dilutes the concentration of pollutants, rendering the cleaning effect of a few houseplants almost negligible. Subsequent scientific reviews and calculations have suggested that you would need a forest-like density of plants—some estimates say hundreds or even thousands in a single room—to meaningfully replicate the air-cleaning effects seen in the sealed NASA chambers. The study was scientifically valid, but its practical application has been largely overstated.
The Real, Proven Benefits of Houseplants
So, should you get rid of your green companions? Absolutely not. While they may not be the powerful air-purifying machines we once thought, their benefits are still immense. Numerous studies have shown that the presence of indoor plants has significant psychological advantages. They can help reduce stress and anxiety, boost mood, and even improve concentration and productivity. The act of caring for a living thing provides a sense of purpose and a connection to nature, a concept known as biophilia. Plants add beauty, colour, and life to our indoor spaces, improving our overall sense of well-being. Their value is not in turning your home into a sterile environment, but in making it a more pleasant and calming place to be.
