Walking through a pine forest, you instantly notice its fresh, crisp aroma. But replicating that scent indoors with air fresheners, wax melts, and floor cleaners may pose serious health risks due to pollution.
Purdue University engineers have discovered that these products release nanoparticles, tiny enough to penetrate deep into the lungs. These particles form when fragrances react with ozone, which enters buildings through ventilation. This reaction creates new airborne pollutants, potentially harmful to human health.
HOW FRAGRANCES CREATE HARMFUL NANOPARTICLES
A forest is a pristine environment. But using chemically scented products to mimic nature can generate massive indoor air pollution. Nusrat Jung, an assistant professor at Purdue’s Lyles School of Civil and Construction Engineering, warns that these pollutants should not be inhaled.
Nanoparticles, only a few nanometers in size, can reach the deepest parts of the lungs and spread to other organs. Jung and civil engineering professor Brandon Boor are pioneers in studying how these particles form indoors, contributing to our understanding of indoor pollution.
INDOOR AIR QUALITY RESEARCH AT PURDUE
“To understand airborne particles indoors, we must measure them at the nanoscale,” Boor explains. The smallest particles, down to a single nanometer, form when fragrances interact with ozone. These tiny molecular clusters evolve rapidly, filling the air we breathe.
Jung and Boor use the Purdue Zero Energy Design Guidance for Engineers (zEDGE) lab. It is a high-tech tiny house built for air quality research. This residential lab helps track how common household products emit volatile chemicals that transform into harmful airborne particles, leading to indoor pollution.
EVERYDAY PRODUCTS THAT POLLUTE INDOOR AIR
Research shows that many everyday household products may not be as safe as assumed. When released indoors, fragrances react with ozone to form nanoparticles at alarming rates. Scientists have yet to determine the full health impact. Still, high concentrations of these particles raise concerns for respiratory health.
“Scented products don’t just release pleasant aromas,” Jung notes. “They alter indoor air chemistry, forming nanoparticles in concentrations that could harm human health.”
WAX MELTS: THE HIDDEN POLLUTERS
A recent study found that scented wax melts, often marketed as non-toxic, pollute indoor air as much as candles. These products release terpenes, the compounds responsible for their scent. Since wax melts contain more fragrance oils than candles, they emit higher amounts of terpenes.
Terpenes react with ozone, triggering intense nanoparticle formation. Surprisingly, wax melts rival candles in nanoparticle pollution, even without combustion. Other studies confirm that essential oil diffusers, disinfectants, air fresheners, and scented sprays also release large amounts of nanoparticles, adding to indoor pollution.
COOKING AND GAS STOVES: ANOTHER SOURCE OF INDOOR AIR POLLUTION
Scented products are not the only culprits. A study led by Boor found that gas stoves also emit nanoparticles in huge quantities. Burning just one kilogram of cooking fuel produces 10 quadrillion particles smaller than 3 nanometers.
This emission level matches or exceeds the pollution from cars with internal combustion engines. Standing on a busy street exposes you to fewer nanoparticles than cooking with a gas stove indoors.
Still, scented chemical products generate as many, if not more, nanoparticles than gas stoves and car engines. Within 20 minutes of exposure, between 100 billion and 10 trillion nanoparticles could settle in your respiratory system.
INDUSTRY COLLABORATION AND FUTURE RESEARCH
Jung and Boor continue studying indoor air pollution with industry partners. Their lab helps test new air quality measurement instruments before they hit the market.
Companies seek Purdue’s expertise because the tiny house lab mimics real-life settings better than standard testing chambers. One of the advanced tools used is a particle size magnifier—scanning mobility particle sizer (PSMPS) from GRIMM AEROSOL TECHNIK. This device measures nanoparticles as small as a single nanometer, providing high-resolution data on particle formation, helping to study pollution indoors.
COMPARING INDOOR AND OUTDOOR AIR POLLUTION
Breakthrough studies from Purdue compare nanoparticle emissions between indoor and outdoor environments. Indoor air quality is largely unregulated and understudied compared to outdoor air pollution. Understanding these exposures helps improve air quality in homes and workplaces.
Jung’s research also examines how everyday activities, such as hair care routines, impact indoor air. Her team found that cyclic volatile methyl siloxanes, common in hair products, linger in indoor air. A single hair care session can expose a person to 1-17 milligrams of these chemicals, contributing to indoor pollution.
THE NEED FOR STRICTER AIR QUALITY REGULATIONS
Scientists must further explore how inhaling volatile chemicals and nanoparticles affects human health. Jung and Boor hope their findings will improve air quality monitoring and regulation.
“Indoor air quality often gets overlooked, yet it impacts our health daily,” Boor says. “With data from our tiny house lab, we aim to turn research into real-world solutions for healthier indoor environments, reducing pollution exposure.”
FUNDING AND FUTURE DIRECTIONS
Jung and Boor’s work is funded by the National Science Foundation, the U.S. Environmental Protection Agency, and the Alfred P. Sloan Foundation Chemistry of Indoor Environments program. Their research continues to shape the future of indoor air quality management and public health awareness.
