By Edward J. Thomas –
Apparently, people just can’t run inside to protect themselves against air pollutants, especially if they are relying on air fresheners to mask unpleasant smells. Scented products generate indoor pollution, meaning these homes may be loaded with more pollutants than outside environments thanks to the chemicals used in fresheners and sweet-smelling cleaning products.
Purdue University researchers warn that trying to bring in the great outdoors inside through pine-scented or other aroma air fresheners, wax melts, floor cleaners, deodorants and other products only serves to fill the air with nanoscale particles, which are small enough to get deep into lungs.
Air pollution in general is already a significant health concern, as WellWell has reported. Pollution represents an increasing death threat, especially for those over 65. The nanoparticles identified by the Purdue researchers are a bit different. They form when fragrances interact with ozone, which enters buildings through ventilation systems, triggering chemical transformations that create new airborne pollutants.
“A forest is a pristine environment, but if you’re using cleaning and aromatherapy products full of chemically manufactured scents to recreate a forest in your home, you’re actually creating a tremendous amount of indoor air pollution that you shouldn’t be breathing in,” noted Nusrat Jung, an assistant professor at Purdue.
Nanoparticles may be small, but they can do a large amount of damage. A few nanometers in size, these nanoparticles can penetrate deep into the respiratory system and spread to other organs.
“To understand how airborne particles form indoors, you need to measure the smallest nanoparticles—down to a single nanometer. At this scale, we can observe the earliest stages of new particle formation, where fragrances react with ozone to form tiny molecular clusters. These clusters then rapidly evolve, growing and transforming in the air around us,” added Brandon Boor, an associate professor in civil engineering at Purdue.
The Purdue researchers were able to identify the impact of these scented products through the university’s dedicated residential lab space for indoor air quality research. Using industry-developed air quality instruments, they were able to track how household products emit chemicals that evaporate easily, called volatile chemicals, and generate the tiniest airborne nanoparticles.
The team ultimately discovered that many everyday household products used indoors may not be as safe as previously assumed. The specific impact of breathing in these particles has yet to be determined, Purdue’s research has repeatedly found that when fragrances are released indoors, they quickly react with ozone to form nanoparticles. These newly formed nanoparticles are particularly concerning because they can reach very high concentrations, potentially posing risks to respiratory health.
“Our research shows that fragranced products are not just passive sources of pleasant scents—they actively alter indoor air chemistry, leading to the formation of nanoparticles at concentrations that could have significant health implications,” Jung said. “These processes should be considered in the design and operation of buildings and their HVAC systems to reduce our exposures.”
In a recently published paper, the pair found that scented wax melts, typically advertised as nontoxic because they are flame-free, actually pollute indoor air at least as much as candles.
Wax melts and other scented products release terpenes, the chemical compounds responsible for their scents. Since wax melts contain a higher concentration of fragrance oils than many candles, they emit more terpenes into indoor air.
Nanoparticles also come from gas stoves and car engines. Yet scented chemical products match or surpass gas stoves and car engines in the generation of nanoparticles smaller than 3 nanometers, called nanocluster aerosol. Between 100 billion and 10 trillion of these particles could deposit in a person’s respiratory system within just 20 minutes of exposure to scented products.
Ultimately, the university’s research could help support more effective house and building designs in the future.
“Indoor air quality is often overlooked in the design and management of the buildings we live and work in, yet it has a direct impact on our health every day,” Boor said. “With data from the tiny house lab, we aim to bridge that gap—transforming fundamental research into real-world solutions for healthier indoor environments for everyone.”
