Healthcare (Commonwealth Union) – Scents and skincare products do more than influence how a person smells—they actively impact the chemical makeup of the surrounding indoor air, interfering with a vital natural mechanism the body uses to defend itself from air pollution, according to a global team of researchers that includes experts from Penn State.
The research, recently featured in Science Advances, found that everyday items such as perfumes and even fragrance-free lotions can alter the chemical makeup of what’s known as the “human oxidation field”—a protective zone of reactive air surrounding an individual’s skin and breathing space.
According to study co-author Donghyun Rim, an associate professor of architectural engineering at Penn State, these products interfere with how natural skin oils interact with ozone indoors, reducing the formation of highly reactive hydroxyl (OH) radicals. These radicals are essential for maintaining the body’s invisible chemical shield that helps protect against ozone inhalation.
“Think of people as candlelight, our body temperature is typically the warmest thing in the indoor environment,” he 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.”
However, he noted, the outcome might not be entirely positive. The process is intricate: when ozone interacts with the skin, it produces OH radicals, which in turn lead to further chemical reactions that emit additional compounds into the air around us.
Rim pointed out that they do not yet have a complete picture of what these secondary substances do, but they are actively investigating it.
Since people spend as much as 90 percent of their lives indoors, the quality of indoor air significantly influences their overall exposure to chemical contaminants. Simply being in a room where ozone — a widespread pollutant that can seep in from outdoors — is present can cause our bodies to chemically engage with it, he explained.
In their study, the researchers ran tests in which participants sat inside a controlled environment containing ozone. They initially measured the OH levels produced by the individuals without any personal care products. Afterwards, they repeated the tests after the participants applied either a standard unscented body lotion or a well-known fragrance.
The team led by Rim, which played a key role in identifying the human oxidation field in 2022, created a 3D computational fluid dynamics model to track how this field changes over time. This model enabled them to examine how personal care products influence the field.
Their analysis revealed that using such products significantly disrupted the natural oxidation field surrounding the human body. Notably, applying an unscented lotion increased OH reactivity by about 170%, which in turn reduced OH concentrations around the person by approximately 140%. This drop meant the natural ozone-defense layer became less than half as effective, as the OH radicals were released into the air rather than staying close to the skin to form a protective boundary.
The researchers also observed that lotion had longer-lasting effects than fragrance. While fragrances caused a more immediate impact, their influence faded faster because the volatile organic compounds they contain, such as ethanol, quickly evaporated and dispersed widely into the air.
Nora Zannoni, a researcher at the Institute of Atmospheric Sciences and Climate in Bologna and the lead author of the study, pointed out that when fragrance and lotion were used together, the results showed that fragrances affect OH reactivity and concentration over shorter durations, while lotions have longer-lasting effects. This aligns with how quickly organic compounds are released from these types of personal care products.
