Fragrances and lotions don't just change the way people smell; they also disrupt a crucial natural process that protects the body from indoor air pollutants, a new study by an international team of researchers finds.
Personal care products such as perfumes and lotions not only alter a person's scent but actively modify the indoor air chemistry around them, disrupting a natural protective process, according to an international research team.
The findings, published in Science Advances, suggest that these products interfere with the "human oxidation field," a natural air shield produced by the body that helps protect against indoor pollution.
"Think of people as candlelight, our body temperature is typically the warmest thing in the indoor environment," co-author Donghyun Rim, an associate professor of architectural engineering at Penn State, said in a news release. "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."
However, Rim notes that the process is complex. The initial reaction between skin oils and ozone generates highly reactive hydroxyl (OH) radicals, which form an invisible chemical barrier around a person. When personal care products are applied, they disrupt this barrier, leading to significant changes in indoor air quality.
To investigate these effects, the researchers conducted experiments with volunteers in a controlled chamber with ozone present. They measured the natural OH field around the volunteers without any products and then repeated the experiments after applying an unscented lotion or a fragrance.
The results were striking: application of the unscented lotion increased OH reactivity by approximately 170%, resulting in a 140% decrease in the concentration of OH radicals around the skin. This means the natural protective barrier was weakened, making the body more susceptible to ozone exposure.
"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," lead author Nora Zannoni, a former postdoctoral research fellow at the Max Planck Institute for Chemistry and now a researcher at the Institute of Atmospheric Sciences and Climate in Bologna, Italy, said in a news release.
The team, which first identified the human oxidation field in 2022, utilized a three-dimensional computational fluid dynamics model to visualize the changes. They discovered that while the effects of fragrance were immediate and short-lived, those of lotions were longer-lasting due to the slower breakdown of their organic compounds.
Indoor air quality is critical as people spend up to 90% of their time indoors. This research underscores the hidden impacts of everyday personal care products on our environment and health.
Apart from Penn State and the Max Planck Institute for Chemistry, researchers from the University of California, Irvine and the Technical University of Denmark also contributed to the study.