You've probably seen articles claiming houseplants "purify the air" or listing the "best plants for clean air." This idea is pervasive, but the scientific reality is less exciting. Here's what we actually know.
The NASA Study
Most "plants clean air" claims trace back to a 1989 NASA study. Here's what that study actually found:
What NASA Did
Researchers placed plants in small, sealed chambers and measured their ability to remove specific VOCs (formaldehyde, benzene, trichloroethylene) over time.
What NASA Found
Plants did remove some VOCs in these controlled conditions. The study suggested plants might help clean air in space stations.
The Critical Context
- Chambers were very small and sealed
- Real rooms have constant air exchange and continuous pollution sources
- The study wasn't designed to test real-world home conditions
- NASA was looking at sealed spacecraft, not apartments
What Follow-Up Research Shows
Multiple studies since have tested plants in realistic conditions:
The Math Problem
Researchers calculated that you'd need 10-1000 plants per square meter to match what mechanical ventilation or air purification achieves. That's hundreds of plants in a typical room—essentially a greenhouse.
Real-World Testing
Studies in actual rooms (not sealed chambers) show negligible air quality improvement from typical houseplant quantities. The rate of air exchange in normal buildings overwhelms any filtering plants do.
The Consensus
The scientific consensus today: houseplants, in typical numbers, don't meaningfully improve indoor air quality. Opening a window for 30 seconds does more than a room full of plants.
Why the Myth Persists
- The NASA study sounds authoritative
- People want a "natural" solution
- Plant sellers benefit from the claim
- Plants genuinely make spaces feel nicer (psychological, not air quality)
- The truth is less satisfying than the myth
What Plants Actually Do
Psychological Benefits
Studies do show that plants can improve mood, reduce stress, and increase satisfaction with spaces. These are real benefits—just not air quality benefits.
Humidity (Minor)
Plants release some moisture through transpiration. In very dry conditions, many plants might slightly increase humidity. This effect is minimal with typical plant numbers.
Aesthetics
Plants make spaces look better. This is subjective but widely shared.
What Actually Cleans Air
If air quality is your goal, these methods are effective:
- Ventilation: Opening windows exchanges indoor air for outdoor air
- HEPA air purifiers: Mechanically filter particles at meaningful rates
- Source control: Reducing pollution sources in the first place
- Exhaust fans: Remove pollutants from cooking and bathing
Should You Have Plants Anyway?
Absolutely, if you want them. Plants offer:
- Aesthetic improvement
- Psychological benefits
- A hobby and connection to nature
- Something living in your space
Just don't buy them expecting air purification. Buy them because you like plants.
The Honest Answer
If someone asks whether to get plants for air quality: get an air purifier if air quality is the goal, and get plants if you want plants. Don't expect plants to solve air quality problems—they won't.