Perfumes and lotions interfere with the body’s pollution defense

Fragrances and lotions don't just change the way people smell, they actively alter the indoor air chemistry around the wearer, disrupting a critical natural process the body uses to protect itself from pollution, according to an international research team that includes scientists from Penn State.

The new study, published in the journal Science Advances, revealed that personal care products like perfumes and even unscented lotions alter the chemical composition of the "human oxidation field," a natural protective air shield around a person's breathing zone and skin.

The study suggests that the products disrupt how skin oils naturally react with indoor ozone to produce highly reactive hydroxyl (OH) radicals. Those radicals play a key role in forming an invisible chemical field around the person that protects them from ozone exposure, explained Donghyun Rim, associate professor of architectural engineering at Penn State and co-author on the study.

Think of people as candlelight, our body temperature is typically the warmest thing in the indoor environment. 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."

Donghyun Rim, associate professor of architectural engineering at Penn State and co-author on the study

But it may not be completely beneficial, he added. 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 said. "But we're working to understand it."

People spend up to 90% 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, he explained.

In the study, the research team conducted experiments where 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.

They found that applying the products substantially disrupted the natural human oxidation field. Specifically, the application of unscented lotion caused a roughly 170% increase in OH reactivity, which led to a roughly 140% decrease in OH concentrations around the wearer, meaning their natural ozone barrier was less than half as strong because the OH radicals were floating off into the air instead of forming a protective force field.

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, like ethanol, broke down more rapidly into the gas phase and were dispersed more broadly into the air.

"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 news release.

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.