A new study in Science Advances examines how the natural human oxidation field can affect chemical exposures indoors – and how fragrances and personal care products such as body lotions alter these dynamics.
As the article explains, humans generate hydroxyl radicals (OH) in the presence of ozone through skin-emitted alkenes. Lotions containing phenoxyethanol or alcohol-based fragrance, however, were found to increase the reactivity of these radicals, consuming them and thereby reducing their overall concentration.
In vivo Materials and Methods + Simulation Models
Assessments were made using a fragrance-free body lotion containing linoleic acid (Neutral, Unilever body lotion for sensitive skin; 0% colorants and 0% perfume, per the article) and a commercial fragrance including linalool, a terpene alcohol present in lavender (CK One by Calvin Klein). Comparisons were also made combining the lotion and fragrance, and using linalool alone without alcohol.
Measurements were taken with four subjects who first were exposed to O3 in a temperature-controlled indoor chamber, following which they applied the body lotion or fragrance. Then, measurements were repeated.
"Combining air measurements from within the chamber with model simulations, we determined the net effect of the lotion and fragrance on the human oxidation field," the authors wrote.
Reaction and Consumption Dynamics
Beyond the lotion and fragrance increasing OH reactivity and decreasing OH concentrations, the authors observed additional dynamics.
Body lotion: The body lotion was found to suppress the production of 6-methyl-5-hepten-2-one, an OH precursor. It also "enhanced OH losses in the gas phase."
What's more, the linoleic acid in the body lotion reacted with OH. Plus, the application of the lotion was said to "effectively dilute the concentration of squalene on the skin surface available for reaction, thereby obstructing the O3-skin reaction."
Fragrance: The authors noted that while fragrances contain terpenes that can generate OH, their larger ethanol concentration reportedly acted as "a large OH sink." Indeed, linalool alone without ethanol was tested and increased reactivity initially, but only reduced the OH concentrations by less than 10%.
Lotion + fragrance: Finally, applying both the fragrance and lotion revealed that fragrances affected the OH reactivity and concentration more quickly, while lotions showed more persistent effects, "consistent with the rate of emissions of organic compounds from these [personal care products]."
"These findings have implications for the indoor chemistry of occupied spaces and human health," the authors concluded.
What implications could these findings have for the industry? Another layer of safety testing? Or could we spin this into a new "protective"-type claim? We asked a few industry experts for their insights.
New Focus On and Around Skin?
"As humans, we live in an environment full of oxidative insults both for the external and internal body," said dermatologist Zoe Draelos, M.D. "External oxidative insults include UV radiation, pollution and tobacco smoke. However, humans possess an oxidative field around them that interacts with the atmosphere and any topical skin care products."
She added that antioxidants are incorporated into many skin care products and can effectively reduce the inflammatory effects of UV radiation – but skin care products may also be able to quench reactive oxygen species (ROS) in the atmosphere around humans.
"Typically, we focus on what is on the skin, but we may also need to focus on what is in the air surrounding the skin. Personal care products can place a protective layer over the skin and also positively impact the atmosphere contained in our personal space."
