Do Houseplants Really Work as Air Purifiers?

The question sounds straightforward. Yet once you look closely at the measurement science underneath it, the real answer is more nuanced than either "yes" or "no".

Where the houseplant air purifier claim began (NASA, 1989)

The popular notion of the houseplant-as-air-purifier largely traces back to a 1989 US study carried out for NASA, linked to research on closed-loop life-support systems for space stations.

Working in sealed, tightly controlled chambers, researchers found that certain plant species could lower concentrations of volatile organic compounds (VOCs). VOCs are chemicals that readily evaporate into the air at room temperature, and the group includes some harmful substances such as benzene, trichloroethylene and formaldehyde.

That underlying science was solid. The difficulty comes from extending results from a sealed NASA chamber to the realities of an ordinary living room.

This difference is crucial, and it sits behind much of the overstated reporting about houseplants’ air-cleaning powers that came afterwards.

Many studies that demonstrate pollutant removal by houseplants share the same basic setup: small, sealed chambers where unusually high pollutant levels are added in a single, large dose.

A plant is then put into the chamber, pollutant concentrations are tracked over time, and a removal rate is calculated. This approach is useful for comparing one plant with another.

But it is a poor way to forecast what happens inside a typical home.

What chamber studies miss: the air exchange rate

The key missing factor is what building scientists call the air exchange rate: the speed at which outdoor air naturally replaces indoor air via gaps in the building fabric, walls and ventilation systems.

In real buildings, that ongoing dilution already does much of the work in reducing indoor pollutant concentrations.

When a 2019 study modelled plant performance against realistic air exchange rates, it concluded you would need between ten and 1,000 plants per square metre to equal what passive building ventilation already accomplishes.

So, the most scientifically defensible conclusion is this: houseplants can remove some pollutants, but they are not an effective standalone air-cleaning solution for homes.

That does not mean the early studies were "wrong". Rather, their findings were often pushed into everyday contexts where indoor-air physics operate very differently.

Potted plants vs engineered plant-based systems

Recent review papers also draw a clearer line between ordinary potted plants and more engineered plant-based systems. Some botanical biofilters-which use fans to force air through plant-root substrates-may offer practical air-cleaning potential, but they are a different technology from keeping a few decorative plants on a windowsill.

Another reason the claim is frequently overstated is that indoor environments are not constant. In many chamber experiments, pollutants are released once and then allowed to fall over time in a sealed space.

In homes, by contrast, emissions can be continuous or intermittent-from cooking, cleaning, furnishings, consumer products, heating, and traffic pollution drifting in from outdoors. Temperature, humidity, how many people are at home, and ventilation patterns also shift throughout the day.

All of these variables influence how pollutants are generated, diluted or deposited indoors. As a result, real-world exposure is far more complicated than the controlled conditions in which many plant studies are performed.

What actually improves indoor air quality

For these reasons, the most reliable public health guidance remains fairly simple.

First, reduce or eliminate the source of pollution. That can mean avoiding products that release fumes (such as aerosol sprays or strong chemical cleaners) and fixing building problems-such as damp or leaks-that encourage mould growth.

Next, increase ventilation and use effective filtration. Ventilation can be boosted by, for instance, opening windows and doors, and running kitchen and bathroom extractor fans that vent to the outside.

You can also raise the supply of outdoor air through combined heating, ventilation and air conditioning systems, which can be very effective for filtering air.

Portable air cleaners with high-efficiency particulate air (HEPA) filtration can help lower airborne particle levels, while ventilation-such as opening windows or using extractor fans-helps dilute indoor pollutants when outdoor air quality is acceptable.

Air cleaners differ widely in performance, however.

For everyday use, choose a unit that matches the room size and clearly states it uses a True HEPA filter-meaning it is designed to capture at least 99.97% of very small particles.

It also helps if the device carries an AHAM Verifide label, indicating that its clean air delivery rate (CADR) has been independently tested. As a rough rule, a higher CADR means faster particle removal, and packaging typically states the room size the unit is intended for.

Most air cleaners are built primarily to tackle particles such as dust, pollen, pet dander and smoke.

If you also want support with gases or odours-such as VOCs-look for a model that includes an activated carbon filter, because HEPA filtration alone mainly targets particles. Packaging usually notes whether a unit is designed for particles, gases or both, but no air cleaner removes every pollutant.

It is also worth bearing in mind that plants themselves need proper care. Overwatering and neglected pots can contribute to excess moisture or microbial growth indoors. In that respect, even the upsides of indoor greenery depend on how it is looked after.

Does this mean houseplants are pointless indoors? Not at all.

Even if their direct air-cleaning impact is limited in real homes, plants may still be beneficial.

Research suggests they can improve perceived comfort and psychological wellbeing, and in some situations may slightly affect humidity or the immediate indoor microenvironment.

Keep houseplants because you like them-because they make interiors look better and feel calmer. They can make a home more pleasant, and that matters.

But they should not be promoted as a practical fix for serious indoor air problems.

Pedram Vousoughi, Post-Doctoral Researcher in Biological Sciences, University of Limerick

This article is republished from The Conversation under a Creative Commons licence. Read the original article.

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