Debunking the Myth of NASA’s Air-Cleansing Plants: A Deep Dive into Science and Misinterpretation

Debunking the Myth of NASA’s Air-Cleansing Plants: A Deep Dive into Science and Misinterpretation

The idea that houseplants can dramatically purify indoor air has captured the public imagination for decades. This myth owes its origins to a 1989 NASA study led by Dr B.C. Wolverton, which tested the ability of plants to remove airborne toxins in sealed environments. While the study has been widely cited to promote houseplants as natural air purifiers, the reality is more nuanced, and the findings have been repeatedly misinterpreted. Let’s delve into the science, uncover how this misconception gained traction, and explore what we really know about indoor air quality.

The Original NASA Study: Purpose, Methodology, and Findings

In 1989, NASA partnered with Dr B.C. Wolverton to explore innovative ways to improve air quality in space stations. The closed and artificial environments of space stations necessitate effective methods for removing volatile organic compounds (VOCs), such as benzene, formaldehyde, and trichloroethylene, which are emitted by synthetic materials (Wolverton, 1989). Wolverton’s study tested a variety of common houseplants, including peace lilies (Spathiphyllum), snake plants (Sansevieria), and chrysanthemums (Chrysanthemum morifolium), to determine their effectiveness in sealed experimental chambers.

The study’s methodology involved placing plants in small, airtight containers filled with known concentrations of VOCs. Over 24 hours, researchers measured the reduction in toxin levels, which suggested that plants, in conjunction with their root-associated microorganisms, could indeed remove airborne chemicals. For instance, the peace lily showed the ability to remove benzene and formaldehyde effectively, while the snake plant demonstrated similar capabilities with trichloroethylene.

Key Findings:

• Some plants showed the ability to remove up to 90% of certain VOCs within 24 hours
• Peace lilies were found to be particularly effective, removing 23% of trichloroethylene (TCE) over 24 hours
• Other plants studied included aloe vera, bamboo palm, and mother-in-law’s tongue (Sansevieria)

The study suggested that plants could be an effective means of improving air quality in sealed environments, with NASA researchers stating, “If man is to move into closed environments, on Earth or in space, he must take along nature’s life support system”.

However, this experiment was conducted under highly controlled conditions that bear little resemblance to real-world homes or offices. The small, sealed chambers created an environment where plants had a measurable impact, unlike the dynamic and open conditions of most indoor spaces.

From Study to Myth: The Rise of Misinterpretation

The findings of the NASA study quickly spread beyond academic circles, popularised by media outlets and later by books such as Wolverton’s How to Grow Fresh Air: 50 Houseplants that Purify Your Home or Office (1997). The idea that houseplants could “clean” your home’s air became a staple of lifestyle blogs, advertising campaigns, and even nursery promotions. Over time, this narrative was repeated so often that it became an accepted truth.

However, this oversimplification ignored the critical context of the study. Wolverton himself clarified that the research focused on space stations, not typical Earth environments. The media’s exaggeration overlooked the crucial role of experimental conditions, such as the sealed chambers, which are vastly different from the open, ventilated spaces of homes and offices. Additionally, the scale of impact—a single plant removing significant amounts of toxins—was grossly overstated.

The Science Strikes Back: Debunking the Myth

By the mid-2010s, scepticism about the air-purifying claims of houseplants began to grow. In 2019, Michael Waring and Bryan Cummings published a paper titled “Potted Plants Do Not Improve Indoor Air Quality: A Review and Analysis of Reported VOC Removal Rates.” Their analysis found that the removal rates of VOCs by plants in real-world conditions are negligible compared to the natural air exchange in buildings (Waring & Cummings, 2019). For instance, in a typical home with reasonable ventilation, the air is replaced multiple times per hour, effectively diluting VOC concentrations far more efficiently than any single houseplant could.

Key Points from Waring’s Study:

• The rate at which plants remove VOCs is far slower than the standard air exchange rate in buildings
• To match the air-cleaning capacity of a building’s air handling system or a few open windows, one would need between 100 and 1,000 plants per square meter of floor space
• Natural ventilation is far more effective at cleaning indoor air than plants, and at a much quicker rate

Experimental Conditions vs. Real-World Environments

The stark contrast between the NASA study’s findings and real-world effectiveness can be attributed to the vast differences in experimental conditions:

NASA Study Conditions:

• Sealed chambers, often with a volume of a cubic meter or smaller
• Controlled airflow
• Single VOC injected and tracked over hours or days

Typical Indoor Environments:

• Open spaces with higher air exchange rates
• Multiple sources of VOCs
• Constant introduction of outdoor air through ventilation

These differences highlight why the NASA study’s results cannot be directly applied to homes and offices. In real-world settings, the natural or mechanical air exchange in buildings dilutes VOC concentrations much faster than plants can extract them

Environmental scientists and publications like Vox played a key role in addressing the misinformation. Vox‘s 2019 article explained how the conditions of the NASA study—sealed chambers with no air circulation—created results that are not replicable in open environments. The article also highlighted how perpetuating the myth misleads consumers into believing that a few plants can replace proper ventilation or modern air filtration systems (Vox, 2019).

Comparing Conditions: NASA vs Real Life

The disparity between the experimental setup of the NASA study and the realities of indoor environments is critical to understanding the myth. In the sealed chambers used by Wolverton’s team, plants were placed in spaces with zero air exchange, allowing any removal of VOCs to have a measurable impact. These conditions are akin to space stations, where air is recycled and purified within closed systems.

In contrast, most homes and offices are open systems with multiple sources of airflow, including windows, doors, and HVAC systems. Air exchange rates in such spaces dilute VOC concentrations far more rapidly than any plant’s absorption capacity. To match the impact observed in the NASA study, one would need hundreds of plants in a small room—an impractical solution by any standard.

Practical Science for Better Indoor Air Quality

While houseplants offer aesthetic and psychological benefits, such as reducing stress and improving mood, they are not a substitute for effective air purification. For those looking to improve indoor air quality, practical steps include:

• Using air purifiers: Modern HEPA and activated carbon filters are far more effective at removing VOCs and particulate matter (EPA, n.d.).
• Increasing ventilation: Opening windows and using exhaust fans can significantly reduce indoor pollutant levels.
• Reducing sources of VOCs: Opt for low-emission paints, furniture, and cleaning products.
• Maintaining humidity levels: Proper humidity control can reduce the prevalence of mould and dust mites.

Can Houseplants Harm Our Indoor Air Quality?

While houseplants are often celebrated for their aesthetic and psychological benefits, they can potentially impact indoor air quality negatively. However, similar to the research on their air-purifying benefits, any harmful effects would likely require a significant number of plants to produce notable indoor pollution. Here’s a detailed breakdown of how houseplants might be harmful and practical tips to mitigate these effects:

1. Mold Growth from Overwatering

• Cause: Overwatering houseplants can lead to excess moisture in the soil, which promotes mold growth. Mold spores can become airborne and exacerbate respiratory issues such as allergies and asthma.
• Severity: The mold on a few houseplants is generally far less harmful than larger patches of mold caused by water damage in a home. However, it can still be a concern for sensitive individuals.
• Prevention Tips:
  • Avoid overwatering your plants; water only when the soil is dry to the touch.
  • Ensure proper drainage by using pots with drainage holes.
  • Promote air circulation around the plants to reduce excess humidity.

2. Dust Accumulation on Leaves

• Cause: Dust can settle on plant leaves and later become airborne, contributing to indoor air pollution. This dust can irritate the respiratory system, worsen conditions like asthma and chronic obstructive pulmonary disease (COPD), and exacerbate allergies. Moreover, dust particles may carry harmful pollutants like pesticides or lead.
• Impact: If left unchecked, dusty plants can contribute to a less healthy indoor environment, especially for individuals with pre-existing respiratory issues.
• Prevention Tips:
  • Gently clean the leaves of your plants with a damp cloth on a weekly basis.
  • Regular cleaning prevents the buildup of dust and keeps your plants healthy.

3. Pests on Houseplants

• Cause: Houseplants, especially newly purchased ones or those moved indoors from outdoor environments, may harbour pests such as aphids, spider mites, or mealybugs. While there’s no direct research on how these pests affect indoor air quality, their waste and body parts could potentially become airborne and trigger respiratory issues.
• Prevention and Management:
  • Inspect plants for pests before bringing them indoors.
  • Use non-chemical pest control methods first:
    • Handpick pests off the plant.
    • Remove infested parts of the plant.
    • Spray pests off with water.
  • If non-chemical methods fail, use low-chemical alternatives like insecticidal soaps, horticultural oils, or botanical insecticides such as neem oil.

4. Pollen, Spores, and Fragrances from Plants

• Cause: Certain houseplants and flowers release pollen, spores, or strong fragrances, which can trigger allergic reactions or worsen symptoms for allergy-prone individuals.
• Notable Plants to Watch:
  • Plants known to worsen allergies include ferns, weeping figs, yuccas, palms (male plants), African violets, orchids, and chrysanthemums.
• Better Alternatives:
  • Opt for plants with large, smooth leaves and no flowers, as these are less likely to release allergens into the air.
  • Examples include snake plants, peace lilies, or pothos.

While houseplants can potentially introduce some minor risks to indoor air quality, these risks are generally manageable with proper care and maintenance. The benefits of houseplants, such as their calming presence and contribution to interior design, often outweigh these concerns when practical steps are taken. To minimise any negative effects:

• Avoid overwatering and ensure proper drainage to prevent mold growth.
• Keep leaves clean and free of dust to reduce respiratory irritants.
• Manage pests with low-chemical solutions and inspect plants before bringing them indoors.
• Choose plants that are less likely to release allergens, focusing on foliage plants without flowers.

By taking these precautions, you can enjoy the aesthetic and psychological benefits of houseplants without compromising your indoor air quality.

Conclusion: Appreciating Plants for What They Are

The NASA study on air-cleansing plants was groundbreaking in its context but has been widely misinterpreted. While it’s tempting to believe that a few houseplants can transform indoor air quality, the science tells a different story. Understanding the limitations of scientific studies and recognising how findings can be distorted is essential in an era of misinformation.

Appreciating Plants for Their True Benefits
While the air-purifying claims of houseplants have been largely debunked, it’s important to recognise the many other benefits they offer:

• Aesthetic appeal
• Psychological well-being
• Connection to nature

Rather than clinging to overstated claims, let’s celebrate houseplants for their real benefits. They bring beauty, joy, and a sense of connection to nature into our living spaces. By combining plants with practical measures for air purification, we can create healthier, more harmonious homes that embrace both science and the serenity of greenery.

References

1. Wolverton, B. C. (1989). “Interior Landscape Plants for Indoor Air Pollution Abatement.” NASA Clean Air Study.
2. Wolverton, B. C. (1997). How to Grow Fresh Air: 50 Houseplants that Purify Your Home or Office. Penguin Books.
3. Waring, M. S., & Cummings, B. E. (2019). “Potted Plants Do Not Improve Indoor Air Quality: A Review and Analysis of Reported VOC Removal Rates.” Journal of Exposure Science & Environmental Epidemiology, 29(1), 1–7.
4. Vox. (2019). “Houseplants Don’t Actually Clean the Air Much.”
5. U.S. Environmental Protection Agency (EPA). “Volatile Organic Compounds’ Impact on Indoor Air Quality.” https://www.epa.gov/indoor-air-quality-iaq/volatile-organic-compounds-impact-indoor-air-quality