A 2017 Each Breath Blog post, “Getting into the Weeds: Do Houseplants Really Improve Air Quality?” stated that the jury is still out on whether houseplants reduce indoor air pollution, but the verdict is now in: houseplants do not improve air quality. Here’s why.

The commonly held belief that plants clean indoor air can be traced back to the seminal 1989 NASA study discussed in our previous blog post. This landmark study set out to find out if plants can clean the air in sealed environments, like a space station. Researchers found that in addition to absorbing carbon dioxide, common houseplants can also remove volatile organic compounds (VOCs).

Since then, dozens more research studies have come to similar conclusions: houseplants can reduce pollutants in the air – namely, VOCs like formaldehyde and benzene which are known to cause a multitude of health problems, including respiratory problems and cancer.

However, a 2019 meta-analysis review looked at decades-worth of research on this topic and concluded something different. In their study, named “Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies,” researchers found that to achieve the same benefits seen in other research studies, you would need 10-1,000 plants per square meter of floor space in your home, office or other indoor environment. To reach this number, researchers used past research observations, standardized the metrics, and extrapolated the findings to larger rooms and a larger number of plants. They found that the natural ventilation of a building would be doing most of the work of removing indoor VOCs, rather than the plants themselves. That is, unless you have 680 plants in your 1,500 square foot home or office.

“Challenge Accepted” - plant lovers everywhere

10-1,000 plants per square meter would be required to achieve the VOC-reduction results that many research studies demonstrate.

Where’s the Disconnect Between These Research Studies and Real-Life?

While research offers promising evidence for the potential of plants in mitigating indoor air pollution, it's important to remember that these studies are conducted under strict laboratory conditions.  Typical experiments include placing a potted plant inside a small, airtight chamber and injecting a singular VOC into the air. Researchers measure the level of that VOC at the beginning of the experiment and track how the concentration decreases over time – often over the course of hours or even days. Clearly, these are not real-world conditions. Our indoor spaces are significantly larger than these sealed chambers and many more VOCs are present simultaneously in our indoor environments.

Also, our indoor air is constantly being replaced with fresh, outdoor air. This air exchange occurs through infiltration (cracks or openings in walls, floors, around windows and doors), natural ventilation (open doors and windows), or mechanical ventilation (fans and mechanical systems like HVAC systems). Even “tight” buildings – that is, buildings that are built to conserve energy with features like heavy insulation and windows that don’t open – have more air exchange than the sealed chambers of research studies.

Few studies have looked at the impact of plants within a natural, indoor environment. Those that do exist have faced challenges, including inaccurate measuring equipment and failure to control or measure the air exchange rate. It is therefore impossible to know if the results from these studies (which generally show nominal reductions in VOC concentrations) can be attributed to the plants or air exchange.

Can Houseplants Harm our Indoor Air Quality?

Maybe, but similar to the research on the benefits, it probably would take a lot of plants to produce harmful air pollution. Here’s how they can be harmful and what you can do about it:  

  • Overwatering plants can lead to mold growth on the soil. When mold becomes airborne, it can trigger allergies and asthma symptoms. Mold showing up on a few houseplants is not as harmful as large patches of mold around the home from water damage. To reduce mold growth, avoid overwatering your plants, ensure your plants have proper drainage and make sure to provide enough air circulation.
  • Dust can accumulate on leaves and be distributed into the air. Dust can cause respiratory problems and worsen asthma, COPD and allergy symptoms, but it can also carry toxic pollutants like pesticides and lead.  Gently dust the leaves with a damp cloth weekly.
  • Newly purchased houseplants or plants that have been outside can sometimes have pests like aphids, spider mites and mealybugs. There’s no research on the impact of these types of pests on indoor air quality, but it’s possible that their waste and body parts can become airborne and cause respiratory issues. Use non-chemical control options first – handpick pests, remove the infested part of the plant and spray pests off with water.  If those don’t work, use low-chemical options like insecticidal soaps and oils or botanical insecticides like neem oil.
  • Some plants and flowers can release pollen, spores or fragrances that can cause allergic reactions. Certain plants, including Ferns, Weeping Figs, Yuccas, Palms (male), African Violets, Orchids, and Chrysanthemums may make allergies worse.  Generally, plants with big leaves and no flowers are better options.

If Plants Aren’t the Answer to Cleaner Indoor Air, What Is?

It’s best not to rely on your Pothos or Monstera to clean your indoor air. A better bet is to use proven methods to reduce indoor air pollution. They are:

  1. Source control: reduce pollution indoors by eliminating pollution sources. Everyday household products like cleaning products, air fresheners, glues, permanent markers, cosmetics and paints can contain high levels of VOCs. Eliminate or reduce use of these VOC-containing products to reduce indoor air pollution.
  2. Ventilate: indoor air can be 2-5 times more polluted than outdoor air. Increase ventilation by opening doors and windows for 10-15 minutes each day to bring in fresh, outdoor air to dilute the polluted indoor air.  
  3. Air Cleaning: use mechanical means to filter out particulates from the air. Change furnace filters at least once every 2-3 months and upgrade to a MERV 13 filter if able.  This higher MERV rating helps to capture the smallest of pollutants like viruses.  Use a portable HEPA air cleaner which can remove 99.97% of particulates from the air.   You can build your own DIY Air Cleaner using basic supplies.

To learn more about your indoor air, visit: www.Lung.org/Clean-Air.

Freedom From Smoking Clinic
Detroit, MI | May 29, 2024