Houseplants do not clean the air in a home in any meaningful way, and they do not add a useful amount of oxygen. The better-supported benefits are smaller and more personal. Studies suggest that having plants around can give a modest, short-term lift in mood and comfort, and many people enjoy caring for them.
That is a smaller claim than the one on most plant tags. It is the honest one, and it is still a good reason to grow plants.
Claim: houseplants purify the air
What the research says: not in a real home.
This claim traces back to a 1989 NASA study led by B.C. Wolverton. Researchers put plants in small sealed chambers, added chemicals such as benzene and formaldehyde, and measured the drop over time. The levels fell, and lists of “air-purifying plants” have circulated ever since.
A sealed chamber is not a house. A house is far larger, and outdoor air leaks in and out of it all day through gaps, fans, and open doors. That air exchange removes airborne chemicals much faster than plants can.
In 2019, researchers Bryan Cummings and Michael Waring reviewed decades of chamber studies in the Journal of Exposure Science and Environmental Epidemiology. They calculated that it would take somewhere between 10 and 1,000 plants per square meter (about 1 to 100 per square foot) of floor to match the cleaning that normal ventilation already provides. No home has that many plants.
What does work:
- Opening windows when the weather allows
- Running the range hood when you cook and the bathroom fan when you shower
- Removing the source, such as strong cleaners, scented products, or smoke
- A portable air cleaner with a HEPA filter for dust, pollen, and smoke particles
- Changing the furnace filter on schedule
More detail is in do houseplants purify the air.
Claim: houseplants add oxygen
What the research says: true in a technical sense, but too little to matter.
Plants make oxygen during photosynthesis. Indoor plants grow slowly in weak light, so they make little. The air is already about 21% oxygen, and fresh air moves through a house all the time. A few pots, or a few dozen, do not change the oxygen level in a room.
The related worry that plants “steal” oxygen in a bedroom at night is also unfounded. See how much oxygen do houseplants produce.
Claim: houseplants raise humidity
What the research says: a little, right around the plants.
Plants release water vapor through their leaves, and wet soil evaporates. A dense group of leafy plants can raise humidity slightly in the air right around them. In a house with a furnace running in a cold winter, that effect is small and local. It will not turn a dry room into a comfortable one.
If you want higher humidity for your skin, your woodwork, or your ferns, a humidifier does it. See how to increase humidity for houseplants in winter.
Claim: houseplants improve mood and lower stress
What the research says: probably a little, with weak evidence.
This is the area with the most positive findings. A number of small studies have found that people in rooms with plants report feeling calmer, more comfortable, or in a better mood than people in rooms without them. Some studies of gardening and plant care report similar results.
There are real limits to this research:
- Most studies are small and short. Many last minutes or hours, not months.
- Many rely on people rating their own feelings.
- People can see the plants, so they know which group they are in. That can shape their answers.
- Results vary. Some studies find no effect.
A fair summary: many people feel a bit better with plants around, and the research is consistent with that. Houseplants are not a treatment for any health condition, and no one should use them in place of care from a doctor.
Claim: houseplants make you more productive
What the research says: mixed.
Some office and lab studies report better attention or task scores when plants are in the room. Others find no difference. The studies differ in the tasks, the number of plants, and how long people were observed. A plant on a desk is pleasant. The evidence does not support a promise of better work.
Claim: houseplants repel bugs
What the research says: no.
A potted plant does not keep mosquitoes, flies, spiders, or roaches out of a room. Some plants contain oils that repel insects when extracted and concentrated. The living plant on a shelf does not release enough to matter. See do houseplants repel mosquitoes, flies, spiders, and roaches.
Screens, sealing gaps, and removing standing water work.
Claim: houseplants help you sleep
What the research says: no good evidence.
Claims that a snake plant or lavender in the bedroom improves sleep rest on the air and oxygen claims above, or on studies of scented oils and not of potted plants. Plants in a bedroom are safe and pleasant. They are not a sleep aid.
A summary of the claims
| Claim | Verdict | What works for that goal |
|---|---|---|
| Cleans indoor air | Not in a real home | Ventilation, source control, HEPA air cleaner |
| Adds oxygen | Too little to matter | Fresh air |
| Raises humidity | Slightly, close to the plants | A humidifier |
| Improves mood | Small effect, limited evidence | Plants may help. So do daylight, movement, and time outdoors. |
| Improves productivity | Mixed results | No promise |
| Repels insects | No | Screens and sealing gaps |
| Improves sleep | No good evidence | Talk to a doctor about sleep problems |
The benefits that hold up
These do not need a study to be real.
- They look good. Plants soften a room and add color in a long winter.
- They give you something to tend. Watering, pruning, and repotting are small, steady tasks with a visible result.
- You learn. Watching a plant respond to light and water teaches patience and observation. It is a good project with kids.
- They connect people. Trading cuttings is an old habit. See where to get free houseplants.
- They bring green indoors when the ground is frozen. In a cold climate, that counts for a lot from November to April.
- Some are useful. A pot of herbs on a kitchen sill gets used.
The downsides worth knowing
Plants have costs too.
- Pets. Many common houseplants are toxic to cats and dogs. True lilies and sago palm can be deadly. See what “toxic to pets” means for a houseplant.
- Allergies. Mold on damp soil and pollen from some flowering plants can bother sensitive people. See worst indoor plants for allergies.
- Pests. Fungus gnats and other bugs can come home with a plant.
- Water damage. Pots leak on floors and furniture without saucers.
- Cost and time. Plants need regular care, and some are expensive.
How to get the most from your plants
- Buy plants because you like them, not for a health claim on the tag.
- Put them where you will see them every day.
- Start with a few that are hard to kill. See easy indoor plants for beginners that are hard to kill.
- Match each plant to the light you have.
- For clean air, ventilate. For humidity, use a humidifier. For pets, check every plant before you buy.