Keeping your home smoke-free might not be enough to prevent your kids’ exposure to tobacco, a new study suggests.

Thirdhand smoke is the chemical residue from tobacco smoke left behind in dust and on surfaces. Because children touch everything — carpets, tabletops, toys, clothes, etc.— this makes them especially vulnerable.

A team of researchers at San Diego State University and the University of Cincinnati swabbed the hands of children 11 years and younger to measure the levels of nicotine present, an indicator of thirdhand smoke exposure.

More than 97% of the 504 children in the study had some level of nicotine on their hands. More surprisingly, more than 95% of children in non-smoking households still had nicotine on their hands.

“This study filled an important gap,” said Georg Matt, a psychology professor at SDSU and director of the Thirdhand Smoke Resource Center. “We have done a lot of research about thirdhand smoke in private homes, cars, hotels, and casinos, but we haven’t had access to clinical populations.”

Although nicotine was found, the researchers said, parental protections like home and car smoking bans dramatically reduced the amount of nicotine detected.

“One result of this research should be to include thirdhand smoke as part of parental smoking cessation education programs,” said Melinda Mahabee-Gittens, a pediatric emergency physician and clinical researcher at Cincinnati Children’s Hospital Medical Center, who led data collection for the project.

The amount of nicotine on children’s hands also varied by income and race, the researchers found.

Children from lower-income families had significantly more nicotine on their hands than kids from higher-income families. Children of Black parents had higher amounts of nicotine on their hands than children of white or multiracial parents.

“Low-income children and children of Black parents have the most of this involuntary exposure; this is a wake-up call to protect vulnerable children and is an overlooked part of housing disparities,” said Penelope Quintana, a public health professor at SDSU and co-author of the study.

“With COVID, everybody is spending more time indoors and more time at home. If you live in an environment where people smoke or used to smoke, you’re going to be more exposed to thirdhand smoke than you were before,” Matt added. “This study further highlights the importance of the quality of indoor environments.”

The researchers wrote they plan to continue analyzing other markers of thirdhand smoke exposure and to investigate health outcomes.

They said they hope their research will further support stricter smoking bans, remediation practices, and policies requiring real estate agents and landlords to disclose thirdhand smoke levels in homes. The study was published in JAMA Network Open.

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