I own a lot of houseplants, which in its own way has helped get me through my graduate degree. When the COVID-19 pandemic hit during the spring semester of my first year as a Ph.D. student, I was sent home with my in-person lab work canceled for an unspecified amount of time. With little benchwork to do and classes suddenly becoming virtual on a newly popular app called “Zoom”, I gravitated towards developing my life outside of lab and coursework. What began as a small, lucky bamboo plant and a snake plant developed into a full-fledged hobby that has persisted throughout my Ph.D. years. Some species of plants, such as snake and spider plants, are purported online to detoxify the air by removing harmful volatile organic compounds (VOCs). Volatile compounds, which can be colorless and odor-free and are defined in part by their ability to easily evaporate, can quickly invade the air and enter our bodies through our breath. Given the deleterious nature of human consumption of VOCs, an important question arises - just how valid are the claims that some common houseplants can detoxify appreciable levels of harmful VOCs?
The snake plant is a very common houseplant. Easy to take care of and readily available at most plant stores or the vegetation section of home improvement stores such as Lowe’s or Home Depot, these are a typical addition to the home of any plant enthusiast or collector. Additionally, on plant forums online, snake plants are said to detoxify chemicals such as benzene, formaldehyde, trichloroethylene, xylene, and toluene from the air [1]. Current guidelines recommend an exposure limit of 1 ppm (part per million) of benzene over an 8-hour workday, or no more than 5 ppm for any 15-minute period [2], as even short-term exposure can cause headaches, lethargy, and weariness in subjects exposed to 50-150 ppm. Meanwhile, long-term exposure can increase the risk of leukemia [3]. As a pharmacology researcher-in-training, I tend to think about toxicity in terms of dosage and routes of administration and interpret claims about green technology and natural detoxification with a certain degree of skepticism. So, can plants in fact help in lowering the concentration of these dangerous chemicals to non-harmful levels?
A snake plant next to a bed. Source: https://unsplash.com/photos/B6aJYT5wxkk
The claims found on plant-related websites online boasting about the air-purifying properties of plants are, on a surface level, backed by marginal scientific evidence. For instance, one study, which measured the detoxification rates of 28 different common houseplants (including the snake plant mentioned above) against VOCs such as benzene, toluene, octane, trichloroethylene, and α-pinene, found that some plants could reduce the levels of VOCs in the air such that they indeed have the “potential to significantly improve the quality of indoor air” [4]. More specifically, in an air-tight glass jar, a snake plant was described as an “intermediate removal efficiency” plant due to its ability to decrease benzene levels by 1.76 μg per cubic meter of ambient air when normalized to plant surface area. The authors identified the best species to detoxify the air as Hemigraphis alternata, more commonly known as a purple waffle plant. Conditions in the real world, however, likely preclude these conclusions outside of carefully controlled environments.
In an analysis of 12 different studies on the subject, it was found that plants generate an average clean air delivery rate at a mean of .062 μg per cubic meter per plant, which roughly translates to needing 10-100 plants per square meter to achieve the same level of air quality typically observed by the exchange of outdoor and indoor air seen in homes and office buildings [5]. In layman’s terms, these data suggest it would be more beneficial to open a window than to obtain pure air from a collection of plants to reduce VOC levels in one’s home. So, while plants do in fact facilitate the detoxification of harmful impurities, they do not appear do so at a level that justifies the claim that owning houseplants can meaningfully impact the air quality at home. Moreover, in a recent article in The Atlantic, two experts, one a professor in engineering and the other a pollution researcher, each agreed that houseplants do not clean household air to a significant level [6]. In fact, one equated houseplants’ air purification ability to be no greater than that of “an old pair of socks or a baseball cap [hung] on the wall”.
Why then, has this long-standing myth been circulated throughout society? Until researching for this article, I was under the impression that my houseplants provided at least some partial benefit to the air quality in my home. Interestingly, the idea of houseplant-mediated VOC removal originates back to studies by NASA conducted in the late 1980s. NASA scientist Bill Wolverton first investigated the impact ability of houseplants to clean the air of VOCs as a way to naturally clean the air of hermetically sealed environments, such as those on spacecrafts. His report, released in 1989, issued a resounding positive result which ultimately was circulated by media outlets to be a fact applicable to plants in peoples’ homes. Over the years, this seems to have sparked the resulting pop culture belief that owning houseplants leads to healthier indoor air quality.
Monstera deliciosa plant, commonly found in houseplant collectors’ collections. Source: https://upload.wikimedia.org/wikipedia/commons/8/8e/Indoor_Monstera_deliciosa.jpg
Houseplant ownership has increased dramatically over recent years and, as attested by me personally, has ramped up further due to the COVID-19 pandemic. Roughly 70% of millennials refer to themselves as a “plant parent”, owning at least one houseplant [7], and houseplant sales surged 18% over the pandemic. However, this trend is not just observed in younger individuals - the average age of a “plant parent” is 51.8 years old [8]. Furthermore, over 70% of plant owners agree or strongly agree that purchasing plants makes them happier [8]. Besides the possible gratification from the act of shopping, there must be a reason why people have gravitated towards owning plants in recent years.
Many of us don’t need a good greenwashing campaign to convince us of the real benefits of owning houseplants. Despite their inability to sufficiently purify the air in a home, there are still plenty of reasons to own houseplants. For one, plants are known to improve one’s mood, reducing feelings of depression, anger, and increasing serenity [9]. Even in a high-stress environment such as a hospital, plants have been shown to decrease stress and anxiety [10]. Furthermore, plants do statistically increase the humidity levels in a home [11, 12]. Low humidity levels (<10%) can cause dryness of mucosal membranes, increase indoor ozone concentration, produce static electricity, and can even increase viral transmission rates between humans [12]. Thus, while the air detoxification claims are a bit exaggerated for any real significance, houseplants do have some other tangible benefits. Plus, they’re nice to look at and their maintenance can be a fun, rewarding activity, especially when a new leaf emerges or flower blooms.
Edited by Aaron Owji
References
“15 detoxifying house plants for Cleaner Air”. Best of the South Bay. Retrieved (2015): https://bestofthesouthbay.com/15-detoxifying-house-plants-for-cleaner-air/
“United States Department of Labor.” 1910.1028 App A - Substance Safety Data Sheet, Benzene | Occupational Safety and Health Administration, https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1028AppA.
Najah. “Overview of Benzene Toxicity.” The TASA Group, The TASA Group, 5 June 2017, https://www.tasanet.com/Knowledge-Center/Archived-Webinars/ArtMID/475/ArticleID/1251368/OVERVIEW-OF-BENZENE-TOXICITY.
Yang, Dong, S., et al. “Screening Indoor Plants for Volatile Organic Pollutant Removal Efficiency.” Hortsci, American Society for Horticultural Science, 1 Aug. 2009, https://journals.ashs.org/hortsci/view/journals/hortsci/44/5/article-p1377.xml.
Cummings, Bryan E., and Michael S. Waring. “Potted Plants Do Not Improve Indoor Air Quality: A Review and Analysis of Reported VOC Removal Efficiencies.” Nature News, Nature Publishing Group, 6 Nov. 2019, https://www.nature.com/articles/s41370-019-0175-9.
Meyer, Robinson. “A Popular Benefit of Houseplants Is a Myth.” The Atlantic, Atlantic Media Company, 12 Mar. 2019, https://www.theatlantic.com/science/archive/2019/03/indoor-plants-clean-air-best-none-them/584509/.
“Houseplant Statistics in 2022 (Incl.. Covid & Millennials).” Garden Pals, 9 May 2022, https://gardenpals.com/houseplant-statistics/.
Forney, Julie M. “Houseplant Purchasing Trends.” GrowerTalks, 1 Jan. 2022, https://www.growertalks.com/Article/?articleid=25546.
Kuciel, Kris. “The Truth on the Benefits of House Plants.” Dr. Kris Kuciel, Dr. Kris Kuciel, 22 Apr. 2020, https://www.drkriskuciel.com/blog/the-truth-on-the-benefits-of-house-plants.
Dijkstra, K, et al. “Stress-Reducing Effects of Indoor Plants in the Built Healthcare Environment: The Mediating Role of Perceived Attractiveness.” Preventive Medicine, U.S. National Library of Medicine, Sept. 2008, https://pubmed.ncbi.nlm.nih.gov/18329704/.
Gubb, C., et al. “Can Houseplants Improve Indoor Air Quality by Removing CO2 and Increasing Relative Humidity? - Air Quality, Atmosphere & Health.” SpringerLink, Springer Netherlands, 4 Sept. 2018, https://link.springer.com/article/10.1007/s11869-018-0618-9.
Kerschen, Eric W., et al. “Evapotranspiration from Spider and Jade Plants Can Improve Relative Humidity in an Interior Environment.” Horttech, American Society for Horticultural Science, 1 Dec. 2016, https://journals.ashs.org/horttech/view/journals/horttech/26/6/article-p803.xml.
