Sometimes accepted wisdom needs a more thorough vetting process. Case in point: If you’ve ever heard that owning plants can improve indoor air quality in your home or office and act as a kind of organic air purifier or cleaner, you may be disappointed to learn that there’s not a whole lot of science to back that theory up. In fact, plants will do virtually nothing for you in that respect.

This botanic bummer comes from Drexel University researchers, who just published a study in the Journal of Exposure Science and Environmental Epidemiology. Examining 30 years of previous findings, Michael Waring, an associate professor of architectural and environmental engineering, found only scant evidence that plants do anything to filter contaminants from indoor air.

Many of these studies were limited, the study says, by unrealistic conditions. Plants would often be placed in a sealed chamber, with a single volatile organic compound (VOC) introduced to contaminate the air inside. While the VOCs decreased over a period of hours or days, Waring found that the studies placed little emphasis on measuring the clean air delivery rate (CADR), or how effectively an air purifier can “clean” the space. When Waring converted the studies' results to CADR, the plants's ability to filter contaminants was much weaker than simply introducing fresh air to disperse VOCs. (Additionally, no one is likely to live in a sealed chamber.)

The notion of plants as natural air filters likely stemmed from a NASA experiment in 1989 which argued that plants could remove certain compounds from the air. As with the other studies, it took place in a sealed environment, which made the results difficult to translate to a real-world environment.

Plants can clean air, but their efficiency is so minimal that Waring believes it would take between 10 and 1000 of them per square meter of floor space to have the same effect as simply opening a window or turning on the HVAC system to create an air exchange. Enjoy all the plants you like for their beauty, but it’s probably unrealistic to expect them to help you breathe any easier.