Houseplants together with the medium in which they are grown can reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. Plants can also remove CO2, which is correlated with lower work performance, from indoor areas.The effect was investigated in one study by NASA for use in space colonies.Plants also appear to reduce airborne microbes, moulds, and increase humidity.However, the presence of plants indoors has also been associated with higher humidity and airborne fungal concentrations.
When CO2 concentrations are elevated indoors relative to outdoor concentrations, it is only an indicator that ventilation is inadequate to remove metabolic products associated with human occupancy. Plants require CO2 to grow and release oxygen when they consume CO2. A study published in the journal Environmental Science & Technology considered uptake rates of ketones and aldehydes by the peace lily (Spathiphyllum clevelandii) and golden pothos(Epipremnum aureum.) Akira Tani and C. Nicholas Hewitt found "Longer-term fumigation results revealed that the total uptake amounts were 30−100 times as much as the amounts dissolved in the leaf, suggesting that volatile organic carbons are metabolized in the leaf and/or translocated through the petiole." It is worth noting the researchers sealed the plants in Teflon bags. "No VOC loss was detected from the bag when the plants were absent. However, when the plants were in the bag, the levels of aldehydes and ketones both decreased slowly but continuously, indicating removal by the plants" ]
While results do indicate house plants may be effective at removing some VOCs from air supplies, a review of studies between 1989 and 2006 on the performance of houseplants as air cleaners, presented at the Healthy Buildings 2009 conference in Syracuse, NY, concluded "...indoor plants have little, if any, benefit for removing indoor air of VOC in residential and commercial buildings."]
Since high humidity is associated with increased mould growth, allergic responses, and respiratory responses, the presence of additional moisture from houseplants may not be desirable in all indoor settings