Michael Miller, 44, does what most smokers do to protect his sons and daughter from the fumes of his Marlboro Ultra Lights. He takes it outside.

After his 7 a.m. coffee, he walks out of his home in Cincinnati to smoke his first cigarette of the day. Then, as a branch manager of a road safety construction company, he smokes dozens more on street curbs.

The tobacco never appears when Miller is coaching on the baseball or football field, or when he’s in the car with his children. But when he’s alone on the road, he sometimes rolls the windows down and lights up.

“I know [cigarettes are] bad,” Miller said. “I know I need to quit.”

New findings highlight the scientific community’s efforts to identify potential dangers of another byproduct of cigarettes that may slip past Miller’s precautions and affect his kids: “thirdhand smoke.”

A recent study in the journal Tobacco Control found high levels of nicotine on the hands of children of smokers, raising concerns about thirdhand smoke, a name given to the nicotine and chemical residue left behind from cigarette and cigar smoke that can cling to skin, hair, clothes, rugs and walls. This thin film can be picked up by touch or released back into the air when disturbed.

The researchers examined 25 children who arrived at an emergency room with breathing problems associated with secondhand smoke exposure.

They discovered the average level of nicotine on the children’s hands was more than three times higher than the level of nicotine found on the hands of non-smoking adults who live with smokers. They said nicotine on the skin of a nonsmoker is a good proxy to measure exposure to thirdhand smoke.

“Because nicotine is specific to tobacco, its presence on children’s hands may serve as a proxy of tobacco smoke pollution in their immediate environment,” the researchers wrote.

They also found that all but one of the children had detectable levels in their saliva of cotinine, a biomarker for exposure to nicotine. All of the children in the study had parents who smoked but did not smoke themselves.

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The high nicotine readings on the kids’ hands, coupled with the “light smoking” habits of the majority of their parents, signaled to lead author E. Melinda Mahabee-Gittens that these toxins could have arrived from a source other than direct access to cigarette smoke.

“Clearly they’re getting it from somewhere, and perhaps it may be this thirdhand smoke connection,” said Mahabee-Gittens, an emergency room physician at Cincinnati Children’s Hospital Medical Center.

Children face a higher risk of developing health complications from thirdhand smoke than adults. Infants tend to spend more time indoors and can be surrounded by contaminated objects like rugs and blankets, according to a 2004 study written by Georg Matt, a professor of psychology at San Diego State University who co-authored the study and has researched thirdhand smoke. An infant’s propensity to place their hands in their mouth increases the likelihood of the young ingesting the toxic residue.

Thirdhand smoke can linger in an area long after a cigarette or cigar is snuffed out — for up to five years, Matt said.

“Tobacco smoke doesn’t go up in the air and it disappears and it’s gone,” Matt said. “That’s the illusion.”

The negative health consequences of secondhand smoke are well-established.

Researchers at the U.S. Centers for Disease Control and Prevention estimate that since 1964 at least 2.5 million nonsmokers have died of diseases linked to their exposure to cigarette smoke.

In contrast, research on thirdhand smoke gained popularity only a decade ago, but multiple studies suggest the mix of toxins can lead to adverse health outcomes. An animal model simulating thirdhand-smoke-contaminated homes found the chemicals harmed mice’s livers, lungs and healing abilities. A separate 2010 study showed thirdhand smoke mixed with nitrous acid — a gas sometimes emitted from leaky gas stoves — can form cancer-causing chemical compounds. These toxins have also been shown to damage human DNA.

“All in all, I think the evidence that we’ve gathered is basically pointing to potentially high levels of risk to young children and toddlers, and also expectant mothers,” Anwer Mujeeb, program officer for the Tobacco-Related Disease Research Program.

Unfortunately, removing thirdhand smoke from a child’s environment is no easy task. The variety of compounds that make up cigarette residue react to cleaning products differently, Matt said, making it difficult to purge a space of pollutants.

Governments and agencies across the nation have attempted to curb the threat of smoke exposure by implementing tobacco bans. Forty-one states and the District of Columbia have implemented local smoke-free laws, according to the lobbying group Americans for Nonsmokers’ Rights.

Although the majority of these laws are meant to address secondhand smoke exposure, an unintended benefit of the ordinances is a reduction in thirdhand smoke, said Stanton Glantz, professor of medicine and director of the Center for Tobacco Control Research and Education at University of California-San Francisco.

Reynolds American Inc., the second-largest tobacco company in the United States, declined to comment on the study. The Altria Group, the leading U.S. cigarette manufacturer, did not respond to requests for comment.

Mujeeb said more work must be done to better understand the risks of thirdhand smoke. Researchers still do not know the threshold of exposure that leads to harm. Other potential pollutants in the environment need to be identified as well to “properly characterize the risk of thirdhand smoke,” he said.

Miller is skeptical of the threat thirdhand smoke poses to his family, but he is determined to quit smoking this year on his 45th birthday in July. With the help of medicine, he hopes to break the habit his kids remind him is proven to kill.

“I think there’s far worse things that are going on than any tar on my hands,” he said.

This article originally appeared on Kaiser Health News.

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