Toxic Thirdhand Smoke Residue Reaches Many Children Even in Nonsmoking Homes

More than 90% of all children tested showed evidence of exposure, with highest levels found among Black children and those living in low-income and low-education households

CINCINNATI, June 6, 2025 /PRNewswire/ -- Toxic residue from tobacco smoke lingering in dust, old carpets, couches, and other surfaces was found on the hands or in the saliva of more than 900 of the 1,013 children tested in a recent study -- including children living in "smokefree" homes.

The findings, published online May 29, 2025, in Environmental Health Perspectives, also reveal striking gaps in exposure levels based on differences in education, income and race.

Led by E. Melinda Mahabee-Gittens, MD, PhD, from Cincinnati Children's and Georg E. Matt, PhD, from San Diego State University, the study examined hand nicotine and saliva cotinine levels in children aged 11 years and younger. The findings provide the strongest evidence to date that thirdhand smoke residue is a significant, independent source of tobacco smoke exposure for children. 

"The idea that a child is safe from tobacco exposure simply because no one smokes around them is a dangerous misconception," Mahabee-Gittens says. "Our data show that even in homes with strict no-smoking rules, thirdhand smoke pollutants persist on surfaces, in dust, and household objects and accumulate in children's bodies." 

What is Thirdhand Smoke?

Firsthand smoke is the self-exposure that people directly experience by tobacco smoking or vaping. Decades of research have established the direct health risks of smoking, including lung cancer, heart disease, emphysema, and more. 

Secondhand smoke describes other people breathing in toxins from air polluted by smokers. Numerous studies also have shown health harm caused by such exposures, which have led to many indoor smoking bans.

Thirdhand smoke describes exposure to toxic smoke particles and gases that stick to surfaces, become embedded in fabrics, and even saturate drywall. This residue can linger for years. It can be picked up by touch, easily transferred from hand to mouth, and inhaled when it off-gases. Thirdhand smoke residue contains many of the same unhealthy compounds as secondhand smoke.

There is no "safe" level of tobacco smoke exposure. However, the long-term harm caused by thirdhand smoke exposure remains under study.

What does the new study show?

• Widespread Exposure: 94.5% of children living with nonsmokers in homes with strict bans showed detectable nicotine on their hands.
• Racial and Socioeconomic Disparities: The nicotine levels found on child hands varied sharply based on the race, parental education levels and household income. For example, nicotine levels were up to 25 times higher among children in low-income homes (less than $15,000 a year) compared to children in households with incomes exceeding $90,000 a year. Nicotine levels found on the hands of Black children was up to three times higher than that of White children.
• Housing Risks: Children living in older, smaller, and multi-unit homes experienced significantly higher exposure levels, regardless of their parents' smoking status.

What can be done to reduce risk?

The new data exposes a dangerous legacy of tobacco pollution in U.S. housing.

"These results demand a reevaluation of how we assess and address tobacco pollution in homes," Matt says. "We must move beyond secondhand smoke and begin treating thirdhand smoke residue as the persistent environmental hazard it is."

Unlike asbestos or lead paint, no thresholds currently exist for thirdhand smoke pollution, such as notifying incoming tenants or issuing orders to clean up smoke-polluted buildings.

The study authors recommend that policymakers focus on:

• Developing and funding strategies to identify and remediate thirdhand smoke-contaminated homes, especially in low-income housing.
• Enforcing comprehensive tobacco-free housing regulations, especially in multi-unit dwellings.
• Routine screening of children using hand nicotine tests to determine tobacco smoke exposure.

For people living in places where government actions are limited, the co-authors recommend: 

• Avoiding multi-unit housing without a property-wide smoking ban.
• Avoiding housing where previous occupants smoked or vaped.
• Enforcing strict home smoking bans. While results can vary--and some exposure occurs anyway in most cases--the new study shows a consistent reduction in overall nicotine exposure among "protected" groups.

Funding sources for this research included the National Institute of Environmental Health Sciences (NIEHS).

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SOURCE Cincinnati Children's Hospital Medical Center