Personal care products influence the chemistry of the air swirling around us.
Lotion and perfume disrupt chemical reactions that occur between ozone and skin oils, researchers report May 21 in Science Advances. More work is needed to understand how these reactions might benefit or affect human health, they say.
In 2022, atmospheric chemist Nora Zannoni and colleagues discovered that ozone in the air reacts with skin oils to create the “human oxidation field,” a cloud of chemicals called hydroxyl radicals. These molecules react with many other compounds, including pollutants and organic materials in the air, says Zannoni, of Italy’s National Research Council in Bologna.
Following the 2022 study, the team wanted to investigate how commonly applied skin products might influence the human oxidation field, says Jonathan Williams, an atmospheric chemist at the Max Planck Institute for Chemistry in Mainz, Germany. So the researchers had four volunteers apply a moisturizer or fragrance just before entering a climate-controlled chamber, he says. The team added some ozone gas to the chamber, then measured amounts of hydroxyl radicals and other chemicals generated.
Both lotion and perfume lowered the amount of hydroxyl radicals in the chamber compared with when participants wore neither product, the team found, but in different ways.
Lotion dilutes the oils at the skin’s surface, leaving less available to react to form the radicals. Over a few hours, the lotion also releases a chemical called phenoxyethanol, which reacts with radicals that do form.
Unlike the lotion, the perfume — unisex fragrance “CK One” from Calvin Klein — didn’t suppress the formation of new hydroxyl radicals. But when participants applied perfume while in the chamber, the radicals that were already present reacted in a few milliseconds with perfume ingredients — particularly ethanol, which fragrance makers use to dilute and dissolve scented compounds. A hydroxyl radical “is like a wild animal,” Williams says. “All it wants to do is rip the hydrogen off another molecule.” This reaction lowers the amount of hydroxyl radicals near a person’s skin. Once it steals that hydrogen atom from ethanol, the radical becomes a stable molecule of water.
Skin products’ effects on the air in a person’s vicinity might be beneficial, harmful or neutral. It depends on the specific chemical cocktail of the products and the indoor environment, says Linchen He, an environmental health scientist at Lehigh University in Bethlehem, Pa. When the hydroxyl radicals react with other compounds in the air, they produce new chemicals, which could either be safer or more irritating than their precursors, or than the radicals themselves. “More works are needed to identify what chemical could be newly generated” and to understand their potential impacts on health, He says.
Williams agrees. “I don’t think there’s a clear message I can give” about whether people should wear more or less of these personal care products, he says. “We just simply do not know enough about the impact of the various chemical mixtures around us in the indoor environment,” he says. “That’s something which is being researched a lot at the moment … especially the indoor chemistry that we humans invoke just by being in a room.”