What does a clean room smell like? Many people say citrus, pine, or flowers because these fragrances are common in cleaning products. A research team led by Brandon Boor found that scent compounds in cleaning products - conventional and botanical essential oil-based - quickly react in the air, forming nanoparticles that can travel deep into the lungs if inhaled. To reduce exposure to this invisible pollution, the team suggests using unscented products, running exhaust fans, and avoiding ozone-generating devices while cleaning.
The researchers will present their results at the fall meeting of the American Chemical Society (ACS) during the "Healthy Indoor Spaces: Bridging the Microbiome and Chemistry" symposium in McCormick Place. ACS Fall 2026 is being held August 23-27.
"Importantly, cleaning removes viruses and bacteria from surfaces, but it can also generate invisible air pollution. There's no visible dust or smoke in the air, but these particles are forming." - Brandon Boor
"We showed that indoor ozone reactions with fragrances from cleaning produce nanoparticles that carry a respiratory dose comparable to, or greater than, what you would experience from standing outside along a busy road," says Boor, an Assistant Professor of Civil and Construction Engineering at Purdue University who studies indoor air quality. "The particles are different in terms of their composition, but the total dose can be higher. You're not seeing smoke, dust, or haze in the air. Instead, you think the air smells great so it must be clean."
Boor and his colleague Nusrat Jung, a Purdue Assistant Professor of Civil and Construction Engineering, started studying the impact of cleaning products and chemical disinfectants on indoor environments during the COVID-19 pandemic. In that work, they observed that many of these products are heavily scented. "That's often to create a pleasant smellscape in the indoor space," says Boor. "But clean air should not smell like highly concentrated citrus fruit. It should not really smell of anything."
Purdue University photo/Kelsey Lefever
Atmospheric chemists previously established that terpenes emitted by plants, such as pinene from pine trees, react with ozone to create airborne nanoparticles. The nanoparticles aggregate and eventually grow large enough to seed clouds. But in forests, terpene levels are relatively low, so particle formation occurs slowly.
Using scented products indoors releases terpenes as the fragrance compounds evaporate from surfaces or spray droplets. Common terpenes in cleaning liquids include pinene, limonene (lemon), thymol (thyme), and linalool (lavender), and at concentrations much higher than are found naturally outdoors. As a result, airborne terpene levels during cleaning can reach tens to hundreds of times those found in a forest, says Boor.
To study what happens in the process of routine cleaning, the researchers tested scented conventional liquid products and botanical-containing disinfectant sprays and wipes in a model house on Purdue's campus. The tiny house has a working kitchen, wood flooring, and a bathroom. They found that the same chemistry that forms nanoparticles outside occurs inside at faster and at higher concentrations, which has important implications for human health.
Purdue University photo/Kelsey Lefever
Activities such as mopping, spraying countertops, and wiping surfaces with scented products formed billions or trillions of particles, depending on the product used. Most of the particles, called nanoparticles or ultrafine particles, were 1-30 nanometers wide, a size range often missed by at-home air quality monitors. By tracking them, the researchers observed that routine cleaning can generate ultrafine particle pollution at levels above those found outdoors. This poses potential health risks because ultrafine particles are small enough to deposit throughout the airways and deep into the lungs. There, they can contribute to respiratory system irritation and inflammation, or they can potentially enter the bloodstream.
Most surprising to the researchers was how fast the particles formed and grew - it took a matter of minutes. "By the time you finish cleaning up an indoor space, you've already formed a lot of nanoparticles and inhaled them," says Boor.
More recently, Boor and Ernest Blatchley, a Professor at Purdue, found that simultaneously disinfecting air with germicidal far-UV (UV-C) lamps and cleaning surfaces with scented products creates an environment ripe for nanoparticle formation. In fact, the lamps interact with oxygen in the air and generate ozone, raising ozone levels in the tiny home to around 20 to 40 parts per billion, comparable to, though somewhat lower than, levels outdoors at the time of the experiments. The combination of elevated ozone and high terpene concentrations drove even more intense particle formation in the tiny house, raising potential inhalation concerns.
Brian Magnuson
Boor wants these findings to inform consumers' choices, not alarm them, and provides several steps people can take to reduce their exposure while cleaning:
- Choose low-fragrance or fragrance-free products.
- Avoid applying several scented products in the same cleaning session.
- Run exhaust fans or open windows to ventilate the space.
- Do not simultaneously clean surfaces with scented products while using ozone-generating devices, such as far UV-C lamps.
"Importantly, cleaning removes viruses and bacteria from surfaces, but it can also generate invisible air pollution," says Boor. "There's no visible dust or smoke in the air, but these particles are forming."
Boor thanks all the graduate students who have worked with him in the tiny house experiments along with the support of undergraduate students.
The research was funded by a National Science Foundation Faculty Early Career Development Program (CAREER) grant and the Alfred P. Sloan Foundation.
