All those beauty products people buy for their delicious smells may be wreaking havoc on the environment. The personal hygiene products people use daily — shampoo, lotion, deodorant — emit chemicals into the environment as people walk around after using them. A new CIRES and NOAA study found that siloxane emissions (the chemical commonly found in personal hygiene products) are similar in magnitude to vehicle exhaust emissions from rush hour traffic in Boulder, Colorado, USA.

This work, published in the journal Environmental Science and Technology, is in line with other recent findings that chemical emissions from personal care products can contribute significantly to urban air pollution.

D5 Siloxane, short for decamethylcyclopentasiloxane, is added to personal care products like shampoos and lotions to give them a smooth, silky feeling. Siloxane belongs to a class of chemicals called volatile organic compounds (VOCs); once applied, they evaporate quickly. In the air, sunlight can trigger those VOCs to react with nitrogen oxides and other compounds to form ozone and particulate matter–two types of pollution that are regulated because of their effects on air quality and human health.

Matthew Coggon, a scientist at the University of Colorado Boulder, and his colleagues measured VOCs from various locations, and they tracked the concentrations of traffic-related compounds, including benzene, commonly used as a marker of vehicle exhaust, during rush hour.

By studying their data hour-by-hour, the researchers realized siloxane emissions peaked in the morning, when people put on personal care products and went outside into their cars or buses. That’s when benzene emissions went up too. Emissions of both chemicals decreased during the day, then peaked again during the evening commute. The evening peak of siloxane emissions was lower than in the morning, since the personal care products had largely evaporated throughout the day. “That daily pattern of emissions is what’s key,” Coggon said. “It resembles people’s activities.”

This study is part of an emerging body of research that finds emissions from consumer and industrial products are important sources of urban air pollution. A recent study in Science, led by CIRES and NOAA’s Brian McDonald, found that consumer and industrial products, including personal care products, household cleaners, paints, and pesticides, produced around half of the VOC emissions measured in Los Angeles during the study period.

“This study provides further evidence that as transportation emissions of VOCs have declined, other sources of VOCs, including from personal care products, are emerging as important contributors to urban air pollution,” McDonald said.

The new study also demonstrates that siloxane is a good indicator of of the presence of emissions from personal care products. The research team is looking at other chemicals in personal care products that correlate with siloxane, and one likely candidate is fragrance compounds. Coggon predicts they may also spike in the morning, as people commute.

Coggon says, “We all have a personal plume, from our cars and our personal care products. It’s likely that emissions from personal care product also affect the air quality in other cities besides Boulder and L.A. Our team wants to learn more about these understudied sources of pollution.”

In Indian metros, where deteriorating air quality has been a huge source of civic outcry and frustration, the knowledge that our own personal hygiene products may be contributing to the problem may seem less relevant comparatively. But because internal air pollution, especially in small, confined spaces is just as relevant to our long term health, Indian families that think of homes as sanctuaries may want to pay particular attention.