When people are out and about, they leave plumes of chemicals behind them—from both car tailpipes and the products they put on their skin and hair. In fact, emissions of siloxane, a common ingredient in shampoos, lotions, and deodorants, are comparable in magnitude to the emissions of major components of vehicle exhaust, such as benzene, from rush-hour traffic in Boulder, Colorado, according to a new CIRES and NOAA study.