Peace Lilies (Spathiphyllum spp.) are among the most popular houseplants, frequently celebrated for their elegant white blooms and purported air-purifying capabilities. The scientific discourse surrounding their ability to clean indoor air is rooted in the fundamental physiological processes of plants and a landmark scientific investigation.
From a plant's perspective, the removal of volatile organic compounds (VOCs) from the air is not a dedicated cleaning service but a consequence of their normal metabolic functions, primarily photosynthesis and respiration. During photosynthesis, plants take in carbon dioxide (CO2) through microscopic pores on their leaves called stomata. Simultaneously, they can absorb other gaseous molecules present in the air, including certain VOCs like benzene and formaldehyde. Once inside the leaf tissues, these compounds can be broken down by plant enzymes or incorporated into other cellular processes. Furthermore, microorganisms naturally present in the potting soil, within the root zone (the rhizosphere), also contribute to the degradation of airborne toxins, working in a symbiotic relationship with the plant.
The origin of the peace lily's fame as an air purifier is the NASA Clean Air Study, conducted in the late 1980s. The research aimed to find efficient ways to purify air in sealed space stations. In these controlled chamber experiments, peace lilies were shown to be effective at reducing the concentrations of several specific VOCs, including benzene, formaldehyde, and trichloroethylene. The study concluded that certain plants, including the peace lily, could play a role in improving indoor air quality alongside activated carbon filters, which were also part of the experimental setup. It is crucial to note that the conditions of this study were highly optimized, with powerful greenhouse lighting and a sealed environment that does not perfectly replicate the dynamic and complex conditions of a typical home or office.
The peace lily possesses specific physiological traits that make it a relatively effective plant for this process compared to other species. It is a shade-tolerant plant, meaning it can perform photosynthesis and maintain its metabolic functions in lower light conditions typical of indoor spaces, though it will not flower as prolifically. More significantly, peace lilies have a high transpiration rate. Transpiration is the process of water movement through a plant and its evaporation from the leaves. This high rate of transpiration effectively "pulls" more air and the VOCs dissolved in it into the plant through the stomata, increasing the potential for their absorption and breakdown. Its broad, relatively large leaves also provide a substantial surface area for this gas exchange to occur.
While the biological mechanisms are sound and the NASA study provided a scientific basis, the practical air-purifying impact of a single peace lily in a home is a subject of debate among botanists and environmental engineers. The air exchange rate in a typical building—meaning how often indoor air is replaced with outdoor air through ventilation, leaks, and open windows—is vastly different from a sealed laboratory chamber. In many real-world scenarios, this natural ventilation is the dominant factor in determining indoor air quality, potentially overwhelming the effect of a few plants. Therefore, while peace lilies do remove VOCs at a measurable rate, the number of plants required to meaningfully impact the air in an entire room or building would be impractically large according to subsequent analyses of the NASA data. They are best viewed as one component of a broader strategy for a healthier indoor environment, which includes source control and adequate ventilation.
