Living in the city? You may want to swap commercial lotion and perfume for something more natural.
A new study really opened our eyes to what is happening in the air all around us when our skin is exposed to ozone, which can be particularly concentrated in urban air pollution. Ozone can also be high indoors when there’s a high exchange with outdoor air on polluted days, or ozone-generating air cleaners are used. Ozone ravages the human respiratory system and also is now identified as an important source of oxidative stress and reactive oxygen species in the skin. In particular, ozone has been identified as a source of depletion of cutaneous vitamins and lipids. (Protecting The Skin Against Ozone) This study showed that the application of unscented body lotion and perfume, separately and together, reduced our bodies’ natural protection from the harmful effects of ozone in the air.
In most environments, the skin of our bodies acts like a candle. Because heat rises, and our bodies are usually the warmest thing in the indoor environment, warm air next to our skin flows upward, and cooler air from elsewhere in the room comes in to replace it. “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 (also) absorb ozone, which is beneficial because it prevents us from inhaling ozone directly,” says Donghyun Rim, a co-author of the study. (Your Perfume Could Be Destroying Your Body’s Invisible Air Shield)
The skin oil-air reactions are very complex; they would be very difficult to visualize without computer modeling. Rim’s team developed a three-dimensional computational fluid dynamics model to simulate the evolution of the human oxidation field. In general, it shows that our skin reacts with ozone and produces OH radicals, which are catalysts to make secondary chemical reactions in the air. Wearing personal care products, whether they are fragranced or unscented, significantly affects the OH field.
The study monitored the air around four young male adult volunteers who sat in a controlled chamber (approx 25 deg C/77 deg F) in shorts and shirts, 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 (Neutral Body Lotion) to their arms and legs, or a popular fragrance (CK One) only to the back of their hands.
Because of the approximately 21 degree temperature difference between the room and their body temperature, each person created a “thermal plume” that carried air and all reaction products around their skin upwards. After applying the unscented lotion, there was an approximately 170% increase in OH reactivity mainly because phenoxyethanol (a preservative in the lotion) reacted with the OH field. (Personal care products disrupt the human oxidation field) When ozone reacts with squalene (a natural lipid emitted by our skin cells), it produces 6-MHO and 4-OPA. These decreased markedly with the application of the body lotion, because the lotion effectively dilutes the concentration of squalene on the skin surface available for reaction and obstructs the O3-skin reaction.
When the fragrance was applied, there was a large concentration of ethanol formed inside the room, because ethanol is the fragrance carrier. Therefore, overall effect of a scent diluted in ethanol (i.e., any commercial fragrance) is a large loss of our skin’s OH field because of OH reaction with the ethanol, with only small gains from the terpene VOCs present in the fragrance. This loss of the OH field was greater with the fragrance than the lotion, but more short-lived because the ethanol evaporated quickly.
A third, smaller part of the experiment involved applying a natural essential oil to the participants’ skin, which contains linalool. Linalool is a natural terpene alcohol that comprises over 10% of more than 50 essential oils. (Linalool: Terpene Highlight). Linalool reacts rapidly with ozone and OH under the conditions of the experiment, but its net effect on the OH field generated from human emissions indoors was less than 10%.
What does this study teach us? First of all, air chemistry is extremely complex. Secondly, our bodies are amazing and have natural abilities to protect us from air pollutants such as ozone. However, we have to let our skin do its job, and not block it with the wrong products! In urban areas with high ozone, you might want to think twice about using commercial lotions and fragrances, as they reduce skin’s natural ozone barrier by about half, leaving it more exposed to this damaging pollutant. Go for natural: essential oils that give fragrance and moisturization. These have a minimal effect on our skin’s natural ability to protect itself from ozone.
