The Unexpected Respiratory Cost Of A "Clean" Smelling Home
What does a truly clean room actually smell like? If you said citrus, pine, or lavender, you're not alone. But new research suggests the scents most people consider "clean" may be creating an invisible air quality problem of their own.
A research team at Purdue University found that scent compounds in cleaning products, both conventional and essential-oil-based formulas, react quickly in the air to form nanoparticles small enough to travel deep into the lungs. The team is presenting the findings at the American Chemical Society's fall meeting.
The chemistry behind the smell
Atmospheric chemists have long known that terpenes, compounds released by plants, react with ozone in the air to form air pollutants in the form of nanoparticles. Outdoors, this happens slowly, since terpene levels in natural environments are relatively low.
Cleaning products create a different situation. Common terpenes like pinene (pine), limonene (lemon), thymol (thyme), and linalool (lavender) evaporate off surfaces and out of spray droplets at concentrations tens to hundreds of times higher than what's found in nature, explained Brandon E. Boor, Ph.D., associate professor of Engineering at Purdue and lead researcher of the study, in a press release. "Clean air should not smell like highly concentrated citrus fruit," he noted. "It should not really smell of anything."
The tiny house lab
To see this chemistry play out in real time, Boor's team tested scented liquid cleaners and botanical disinfectant sprays and wipes inside a small model house, complete with a working kitchen, wood flooring, and bathroom. They found that mopping, spraying countertops, and wiping surfaces generated billions to trillions of particles, depending on the product.
The particles, mostly 1 to 30 nanometers wide, are too small for most at-home air quality monitors to detect. But the researchers found that routine cleaning drove ultrafine particle levels above what's typically measured outdoors, delivering a respiratory dose "comparable to, or greater than, what you would experience from standing outside along a busy road" and its outdoor air quality concerns, Boor said.
The researchers also found that pairing scented cleaning with germicidal far-UV (UV-C) disinfecting lamps makes things worse. The lamps react with oxygen in the air to generate ozone, pushing indoor ozone levels up. That extra ozone, combined with high terpene concentrations from cleaning, drove even more intense particle formation.
What surprised the team most was how quickly the particle formation happened; it occurred within minutes. "By the time you finish cleaning up an indoor space, you've already formed a lot of nanoparticles and inhaled them," Boor said.
Why size matters for your lungs
Ultrafine particles are concerning because they can deposit deep into the airways and potentially enter the bloodstream, where they may irritate your lungs and contribute to inflammation.
This tracks with existing research: indoor ultrafine particles have been linked to asthma symptoms in children, partly because we spend the bulk of our time indoors, where these particles have room to accumulate. A 2024 review1 on cleaning product chemistry similarly found that exposure to cleaning and disinfecting products is associated with increased respiratory symptoms, including asthma and rhinitis. Separate chemical modeling research has confirmed that terpene-ozone reactions from cleaning products are a real driver of secondary indoor air pollutants.
How to clean without the invisible cost
The researchers are clear that this information is meant to inform and not alarm homeowners, especially because there are practical steps you can take to reduce air pollution in your home. Here are a few simple swaps the the team recommends:
- Go fragrance-free: Choose low-fragrance or fragrance-free products. Check out these low-tox cleaning swaps for inspiration.
- Don't layer scents: Avoid using several scented products in the same cleaning session.
- Ventilate as you go: Run exhaust fans or open windows while cleaning. Afterward, use an air purifier to filter the air. This editor-tested air purifier is one option worth a look.
- Skip the extra ozone: Avoid ozone-generating devices, like UV-C lamps, especially if cleaning with scented products.
- Assess personal care products: Perfumes and scented makeup, hair, and body care, can also increase chemical exposure at home.
The takeaway
While you may associate a fresh scent with cleanliness, the germ-killing and scent are actually completely separate. And only one of them leaves particles behind in the air you breathe.
If your bathroom still smells like a lemon grove an hour after you've wiped it down, treat that as your cue to open a window and rethink the product. If you want to make a change, start looking for a fragrance-free version of the scented cleaner you use most often first.