USNEWS：避免“第三手吸烟”的危险！

ALL IT TAKES IS ONE whiff to confirm it. Maybe you’re out shopping for a car or in the market for a new home when you suddenly take notice – someone has smoked there. No air freshener can cover it, no deep cleaning can remove the lingering impostor. That’s why, says Dr. Jonathan Winickoff, a professor of pediatrics at Harvard Medical School and general pediatrician at MassGeneral Hospital for Children in Boston, “Real estate agents talk about, ‘If you can smell it, you can’t sell it.'” You can feel it, too, health experts note, as sticky nicotine and other chemicals gum up ventilation and adhere to carpet, curtains and walls.

Beyond the unpleasant sensory experience, there’s another reason the residue of smoking – not just the smoking itself or secondhand smoke – is garnering increasing attention: Emerging research from testing cultured human cells to more recent animal studies suggests that so-called thirdhand smoke, a term originally coined by Winickoff’s research team in 2009, could potentially cause health problems in children and adults exposed to it. “Thirdhand smoke is the toxic contamination that remains after the cigarette is extinguished,” Winickoff explains. It coats surfaces, remains in homes where smoking has occurred – even long after it’s ceased – and then gets re-emitted into the air through what’s called off-gassing.

People are exposed to thirdhand smoke in three ways: First, just as you can smell it, you can inhale it, Winickoff says. “Material that remains and coats every surface in an indoor environment where a cigarette is smoked, comes back off that surface – the volatile compounds come off of it, including nicotine – and then get breathed in.” The second way people, particularly young children, are exposed to thirdhand smoke is by ingesting it. For example, babies crawling on the floor or kids playing closer to surfaces, like romping on a couch, touch the residue and put their hands in their mouths. Thirdly, leftover thirdhand toxins from smoking, like from that sticky couch arm, can be absorbed through the skin in the same way a nicotine patch works. “It turns out nicotine goes through the skin and into the bloodstream, and the same phenomenon happens in places where people use a cigarette or an e-cigarette,” Winickoff says.

Previous research found that a compound in thirdhand smoke damages DNA in human cells and adheres to it in a way that could potentially lead to the development of cancer, and subsequent animal studies have found that thirdhand smoke damages the liver and lungs, impedes the healing of wounds and can contribute to hyperactivity. (This research was in mice; but Winickoff points out it’s long been known that secondhand smoke can contribute to hyperactivity and ADHD in children.) Now, research published in March in the online open-access journal PLOS ONE shows that, in mice, thirdhand smoke causes insulin resistance, a precursor to Type 2 diabetes.

“We can’t experiment in humans,” says Manuela Martins-Green, a professor of cell biology at the University of California–Riverside, who led the research. But she says her team tries to, as closely as possible, reflect the situation people might find themselves in. Using data from the U.S. Environmental Protection Agency, the researchers made chambers used in mouse experimentation that reflect the thirdhand smoke “particles the EPA has detected in the home of smokers,” she says. In previous research, Martins-Green says they also looked at the impact of THS on mice over a relatively long period to help guage what the affect might be on people over the long term.

“This is a relatively new area,” says Bo Hang, a staff scientist at Lawrence Berkeley National Lab in Berkeley, California. He led the research that found thirdhand smoke can cause DNA damage and continues to study the potential harmful effects of THS. Hang points out that epidemiological, or population-based, study data doesn’t yet exist in this area, so experts must speculate about the real-world effects of THS on people. “But I think I would say we have pretty solid data from cell lines and from animal studies to indicate thirdhand smoke would cause adverse effects in humans exposed to it,” he says.

Numerous states, including California, now ban smoking in home day care centers – even when the kids aren’t there – to prevent exposure to thirdhand smoke. Winickoff notes that a proposed federal rule by the Department of Housing and Urban Development would make all public housing smoke-free, which would also reduce thirdhand smoke exposure. “We’ve seen in kids quite high levels of nicotine in their blood,” Winickoff says of research on kids living in housing units where smoking had previously occurred, but doesn’t at the time kids live there. “What we find is much higher levels of cotinine, which is the breakdown product of nicotine, compared to kids who are just living in a house without the building being contaminated by thirdhand smoke.”

In this and other ways, he says, the harmful effects of THS are clear: “In my mind the relationship [between thirdhand smoke and adverse health effects] is absolutely proved, because all of the studies looking at secondhand smoke or voluntary tobacco smoke exposure never separate out secondhand smoke with thirdhand smoke.”