You may not realize it, but your shampoo, deodorant, or lotion could be contributing nearly as much urban air pollution as your daily commute. A new study discovered emissions from siloxane, a common ingredient in those personal care products, are similar to those from vehicles in rush-hour traffic.

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A graph showing emissions from siloxane, found in personal care products, and benzene

Are you leaving air pollution-contributing chemicals in your wake? Scientists from the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences (CIRES) led a study published online this month in the journal Environmental Science and Technology that revealed people’s personal care items could be polluting the air.

Related: INFOGRAPHIC: Demystifying “Natural” and “Organic” Labels on Personal Care Products

The scientists were measuring VOCs from a mobile laboratory and the Earth System Research Laboratory roof, tracking concentrations of traffic-related compounds like benzene at rush hour. They saw a peak in the data and one scientist suggested siloxane. He was right. Siloxane emissions correlated with benzene emissions, so the team guessed siloxane might be found in vehicle exhaust. But tailpipe emission testing and roadside measurements revealed that wasn’t the case.

A woman driving a car as seen from the back seat of the vehicle

Siloxane, a volatile organic compound (VOC), is added to lotions or shampoos to impart a silky feel. The VOC evaporates rapidly after being applied, and according to CIRES, “In the air, sunlight can trigger those VOCs to react with nitrogen oxides and other compounds to form ozone and particulate matter.”

The scientists figured out both chemicals could be connected to commuting. In the morning, after people had applied personal care products and headed outside, siloxane emissions peaked, as did benzene emissions as people traveled in cars or buses. The emissions of both chemicals decreased in the day and then peaked once again at the evening commute, although the evening peak was lower for siloxane emissions as many personal care products had evaporated to a great extent.

“We estimate for the city of Boulder, it’s about 3 to 5 kilograms per day of siloxane (D5), and benzene (from motor vehicles), we estimate is about 15 kilograms,” CIRES scientist and lead author Matthew Coggon said. “So it’s about three to five times lower (than vehicles) in terms of total mass. But the emissions that you see in the morning…they’re fairly close, which is the stunning piece. You driving your car, you’re emitting as much siloxane as your vehicle is emitting benzene. That’s the general gist.”

“We all have a personal plume, from our cars and our personal care products,” Coggon added. “In this changing landscape, emissions from personal care products are becoming important.”


+ Environmental Science and Technology

Images via Depositphotos (1,2) and Kathy Bogan/CIRES