UNIVERSITY PARK, Pennsylvania, May 28, 2025 (ENS) – Fragrances and lotions change the way people smell, and new research shows they do much more than that. These personal care products act to alter the indoor air chemistry around the wearer, disrupting a natural process the body uses to protect itself from indoor air pollution, finds an international research team including scientists from Pennsylvania State University.
Perfumes, colognes, and even unscented lotions alter the chemical composition of the human oxidation field, suppressing this “natural protective air shield around a person’s breathing zone and skin,” reveals the new study, published Tuesday in the journal “Science Advances.”
People spend up to 90 percent of their time indoors, making indoor air quality a major factor in humans’ overall exposure to chemical pollutants. Even just by being in a room with ozone, a common air pollutant that can enter indoors from outside, our bodies react with it, explained Donghyun Rim, associate professor of architectural engineering at Penn State and co-author on the study.
The scientists found that these products disrupt how skin oils naturally react with indoor ozone. This reaction produces highly reactive hydroxyl (OH) radicals.
These radicals play a key role in forming an invisible chemical field around a person that protects that person from ozone exposure.
“Think of people as candlelight, our body temperature is typically the warmest thing in the indoor environment,” Rim said. “We’re constantly pulling the air around us toward us, creating chemical reactions in the immediate area around our bodies – a phenomenon we call the human oxidation field.”
“Our skin can absorb ozone, which is beneficial because it prevents us from inhaling ozone directly,” he said, “But it may not be completely beneficial.”
The process is complex: the initial reaction between skin and ozone that produces OH radicals triggers secondary reactions, releasing new chemicals into the air we breathe.
“We still don’t fully understand the impact of these byproducts,” Rim acknowledged. “But we’re working to understand it.”
During the study, volunteers sat in a controlled chamber with ozone present. The researchers first measured the OH field created by the volunteers without using personal care products. Then they repeated the experiments after the volunteers applied either a common unscented body lotion or a popular fragrance.
Rim’s team, which helped discover the human oxidation field in 2022, developed a three-dimensional computational fluid dynamics model to simulate the evolution of the human oxidation field, which made it possible to see the impact of personal care products.
The researchers found that applying the products disrupted the natural human oxidation field. The application of unscented lotion caused a roughly 170 percent increase in OH reactivity, which led to a roughly 140 percent decrease in OH concentrations around the wearer.
This means that their natural ozone barrier was less than half as strong as it was before application of the products because the OH radicals were floating off into the air instead of forming a protective force field around each volunteer.
The researchers found that the effects of lotion tend to be more persistent over time compared to fragrance. The fragrance effects were stronger initially but less persistent than lotions, as the organic compounds in fragrances, such as ethanol, broke down more rapidly into the gas phase and were dispersed more broadly into the air than the lotions.
“The application of a fragrance and a lotion together showed that fragrances impact the OH reactivity and concentration over shorter time periods, whereas lotions show more persistent effects, consistent with the rate of emissions of organic compounds from these personal care products,” Nora Zannoni, researcher at the Institute of Atmospheric Sciences and Climate in Bologna and lead author on the study, said in a statement.
Globally, use of personal care products is widespread, with a current estimated annual revenue of US$646.2 billion in November 2024, according to Statista. Such extensive consumption has been shown to affect even outdoor air quality in densely populated regions in North America and Europe.
Given that the human oxidation field influences the chemical composition of air in the breathing zone and close to the skin, the human oxidation field affects our intake of chemicals, which, in turn, affects human health, the study indicates.
The other Penn State co-author on the paper is Youngbo Won, who was a postdoctoral researcher in the Department of Architectural Engineering. Other authors are Jonathan Williams, Nijing Wang, Tatjana Arnoldi-Meadows, Lisa Ernle and Anywhere Tsokankunku of the Max Planck Institute for Chemistry; Pascale S. J. Lakey and Manabu Shiraiwa of the University of California, Irvine; and Charles J. Weschler, Gabriel Bekö, Pawel Wargocki of the Technical University of Denmark.
The Alfred P. Sloan Foundation funded the Penn State aspects of this research.
Featured image: Woman with perfume. The global revenue of fragrances is forecast to increase from about US$60 billion in 2024 to US$73 billion by 2030. (Photo courtesy GRETE Fashion Brands via Businesswire)
