People’s beliefs about the health effects of “third-hand smoke” are positively correlated to the extent to which smoking in their homes is prohibited, according to a recent Harvard study.

“Third-hand smoke,” a term coined by the study’s authors, is defined as the smoke that remains after a cigarette is extinguished.

The study, which was led by Jonathan P. Winickoff, an assistant professor of pediatrics at the Medical School and Massachusetts General Hospital for Children, sought to uncover the health beliefs of adults about the inhalation of third-hand smoke and how those beliefs vary across smokers and nonsmokers.

Although the researchers found a positive correlation between opinions about the health impacts of third-hand smoke and prohibiting smoking in the home, the two factors are independently associated.

“We knew that parents thought that second-hand smoke was harmful to their children,” Winickoff said. “But we needed a way to capture the idea that just because the smoke wasn’t visible, it was still harmful.”

Crawling babies and toddlers are especially susceptible to third-hand smoke, as they tend to be closer to contaminated surfaces, Winickoff explained. He added that because children weigh less, toxins that they inhale affect them more than they do adults.

Winickoff and his colleagues collected their data through a national random-digit-dial telephone survey from September to November 2005. Their analysis of the gathered data revealed that 65.2 percent of nonsmokers said they thought that third-hand smoke harms children, compared 43.3 percent of smokers. Additionally, 95.4 percent of nonsmokers said they thought that secondhand smoke is damaging to children’s health, compared to 84.1 percent of smokers.

The researchers also found that nonsmokers’ households were more likely to enforce strict rules against smoking in their homes than those of smokers—88.4 percent versus 26.7 percent.

They concluded that emphasizing that third-hand smoke harms children’s health may be important in persuading adults to prohibit smoking at home, Winickoff said.

Joan Friebely, one of the study’s co-authors, as well as an instructor at HMS and a researcher at the Center for Child and Health Policy at Mass. General Hospital, said she was not surprised about the study’s results.

“It should give another reason to protect their kids and other friends and family from smoking and may also help them quit smoking,” Friebely said.

—Staff writer Marianna N. Tishchenko can be reached at mtishch@fas.harvard.edu.