The health dangers of cigarettes are old news. The potential harm caused by secondhand smoke (SHS) is well known too, but until recently, thirdhand smoke (THS) seemed like a phrase made up by enthusiastic anti-tobacco campaigners. No longer. THS can cause DNA damage in human cells, according to new research from scientists at the Lawrence Berkeley National Laboratory (LBL) in California.

Think of THS as the ghost of cigarettes past. If firsthand smoke comes from directly smoking a cigarette and SHS comes from inhaling someone else’s smoke, THS is what happens when smoke clings to carpets, clothes, skin, furniture, car upholstery, etc., and it poses its own set of health risks. THS contains carcinogens, as well as other chemicals that degrade and can become harmful over time.

“The most affected population now is likely to be children who are living with smokers. That seems to be because the children are the rug rats, they … are rolling around playing on carpeted surfaces that absorb [smoke],” said Lara Gundel, an LBL scientist and co-author of the study, in an interview with Healthline.

The best way to avoid THS is to stop smoking and to make sure that exposed surfaces are cleaned or removed from your home.

“Obviously, it’s something that is very difficult to avoid because smoke even gets on the body, on the skin, hands, and clothes,” Charles Margulis, communications director for the Center for Environmental Health in Oakland, Calif., told Healthline.

Smoking outside seems like a good way to avoid the contamination of THS, but in fact the smoke clings to your body and clothing. “When you go back inside the toxic chemicals are going with you, so obviously that’s very hard to avoid,” Margulis said.

Synthesizing Cigarette Smoke

In a study that was, ironically, funded in part by state tobacco taxes, researchers observed the effects of THS in a cell study, meaning that they examined cells grown in a lab.

Researchers at LBL tested SHS and THS using a box less than 1 cubic meter in volume. Pieces of paper were used to model indoor surfaces like clothing, furniture, and carpets that the gases in cigarette smoke typically cling to.

Five Marlboro Red cigarettes were loaded into ports in the chamber, and about 1 centimeter of each cigarette was smoked over the course of 20 minutes. After the 20-minute period, half of each piece of paper was placed in a sterile, airtight container and frozen, while the remaining half was left in the box for 15 hours before being frozen as well. The paper strips were then analyzed to determine which chemicals clung to them.

Human liver tumor cells were grown and exposed to various levels of the chemicals found in the THS experiment. After analysis, the researchers determined that THS exposure caused widespread damage to the cells' DNA.

Diagnosing the Effects of THS

More research is required to determine the long-term health effects of THS exposure. Middle-aged adults who grew up in an age where cigarette smoke was much more prevalent may well have ailments caused by THS, but at this time, researchers don't know which, if any, biomarkers can indicate this damage.

“There are effects of both SHS and THS that most likely have been there all along, and THS effects have all been attributed to SHS in the past,” Gundel said. The next step in the research process is to find biomarkers that indicate the effects of THS and to conduct studies using animals.

But while the long-term effects are unknown, it’s clear that THS is yet another black mark on the reputation of tobacco. 

“It’s a misconception to think that [tobacco is] harmless. They’re extremely powerful chemicals, especially for kids, that are simple to avoid,” Margulis said.

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