BERKELEY, Calif. — Secondhand smoke is no joke, and it seems that thirdhand smoke is no laughing matter either. A new study by a team at the Lawrence Berkeley National Laboratory reports that hazardous chemicals and nicotine lingering indoors after smoking can cause major long-term health risks to non-smokers who live in these places.
Living in contaminated spaces, whether it’s handling the clothes of a smoker or checking into a cigarette-friendly hotel, seems to be enough to expose someone to toxic chemicals that exceed current risk guidelines, the study says.
Previous work from the same team has looked at the dangers of residual nicotine in the air after smoking or vaping indoors. Results show that indoor surfaces absorb the toxins and react to another airborne compound known as nitrous acid (HONO). The combination creates cancer-causing compounds called tobacco-specific nitrosamines (TSNAs).
Even if you visibly see the smoke clear, a microscopic view shows accumulating nicotine on household surfaces. The continuous nicotine build-up from repeated smoking suggests TSNAs are constantly forming, increasing a person’s risk for developing cancer and other health conditions.
“Since we first described this chemistry in 2010, several studies have further illustrated the presence of TSNAs on indoor surfaces and settled dust. In this new article, we integrated the new information produced over the past decade with our most recent results, to estimate the daily doses to which people may be exposed when living in homes contaminated with thirdhand smoke,” explains Hugo Destaillats, a chemist at the Berkeley lab, in a media release.
How does thirdhand smoke enter the body?
TSNAs enter the body by direct inhalation or by ingesting dust mixed with the carcinogenic compound. While still not completely understood, there is evidence TSNAs can enter through skin contact with polluted air or contaminated surfaces. For example, sleeping on sheets where someone has been smoking. Another method is through epidermal chemistry, where nicotine on the skin reacts with environmental HONO to form TSNA directly on the skin’s surface.
“Nicotine is released in large amounts during smoking, and it coats all indoor surfaces, including human skin,” says lead study author Xiaochen Tang, a researcher at the Berkeley Lab. “We found that the presence of skin oils and sweat on model surfaces led to a higher yield of TSNAs in the presence of HONO, compared with clean surfaces.”
When measuring the doses from each potential TSNA pathway in the body, study authors found the formation of three different TSNAs, including two known carcinogens. One of them, labeled NNA, is not present in tobacco smoke, and there is less information on its toxicity. For this reason, the study focused on the two carcinogens called NNK and NNN.
“We present additional evidence of the genotoxicity of NNA by evaluating its effect on cultured human lung cells,” says Bo Hang, a co-author from Berkeley Lab’s Biosciences Area. “Contact with NNA led to DNA damage, including double-strand breaks, the most deleterious genotoxic outcome.”
The researchers exposed NNK and NNN to the skin of mice, where urine analysis confirmed there were metabolites of the two compounds suggesting they entered the body. Even after the team stopped exposing mice to the carcinogens, they continued accumulating metabolites for another week.
Entry through the skin is a major concern
The findings suggest that repeated exposure to tobacco smoke or vaping can build up toxins in the body, increasing one’s cancer risk. Exposure through the skin seemed to be the route that exposed people more to TSNA and maybe even higher than if the person was smoking themselves.
“These findings illustrate the potential health impacts of thirdhand smoke, which contains not only TSNAs but hundreds of other chemicals, some of which are also known carcinogens,” adds Neal Benowitz, a professor at the University of California-San Francisco. “Next steps for this research will explore in more detail the mechanisms of adverse health effects associated with tobacco and cannabis residues, effective remediation strategies, and translation of scientific findings to tobacco control practice.”
The findings appear in the journal Environmental Science & Technology.