On Aug. 27, 2026, 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 presented their results at the fall meeting of the American Chemical Society

“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.”

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.

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.