Third-hand smoke is “as dangerous as cigarette fumes” according to The Daily Telegraph. The newspaper says that the third-hand smoke that lingers on things like clothes and furnishings can be as dangerous to babies and children as the exposure to second-hand smoke.
The complex research behind these reports is a laboratory study that has demonstrated that new carcinogenic substances develop when a natural substance (cellulose) is first exposed to nicotine and then to nitrous acid in the air. Although the identified compounds could potentially be inhaled, ingested or absorbed through the skin, the study did not measure how much of the substances the body absorbs or their direct effects on a person’s health. The results of these experiments will undoubtedly lead to further research into the health effects of smoke residue.
While it is plausible but unproven that smoke residue could damage health, the dangers of smoking and secondhand smoke are well established. Based on these known dangers alone it seems sensible for smokers to consider the health of others and smoke away from other people, such as outside or in a specially designated room. These types of steps are especially important in households with children and babies.
Where did the story come from?
Mohamad Sleiman and colleagues from Portland State University, University of California San Francisco, and Arizona State University in the US carried out this research. This work was supported by the University of California Tobacco-Related Diseases Research Program and published in the peer-reviewed scientific journal Proceedings of the National Academy of Sciences.
The Daily Telegraph and The Independent have covered this research. Although the newspapers correctly highlighted that the study’s findings are of concern, it is important to note that the extent of any health risks from these compounds has not been assessed by this laboratory research.
What kind of research was this?
Nicotine produced in cigarette smoke is deposited onto indoor surfaces and is reported to persist for week to months. When residual nicotine absorbed onto indoor surfaces reacts with nitrous acid (formed from nitrogen in the air) it produces chemicals called tobacco-specific nitrosamines (TSNAs). The TSNAs produced in this way are believed to be some of the most potent carcinogens present in unburned tobacco and tobacco smoke. Substantial levels of TSNAs have been found on surfaces inside smokers’ cars.
This laboratory research has assessed the formation of harmful TSNA substances on material exposed to smoke by measuring the yield of TSNAs produced when smoke was absorbed by a special cellulose material and exposed to nitrous acid for several hours.
Though the findings of this research are a concern, (which the journalists have rightly identified), the potential health risks to babies and children is only an extrapolation of this laboratory research. In other words, the health risks from ‘third-hand smoke’, or the degree of exposure that would lead to such risks (e.g. proximity to the material or length of exposure needed), has not been directly measured by this study.
What did the research involve?
This was complex laboratory research. In summary, two cellulose substances were exposed to a flow of nicotine vapour in a piece of equipment called a tubular-flow reactor. The nicotine vapour was created by circulating dry air over a beaker of liquid nicotine and humidifying the nicotine air stream. The cellulose was then exposed to the nicotine vapour for periods ranging from 10 minutes to two hours.
After the cellulose had been exposed to the nicotine, it was exposed to nitrous acid vapour created from sulphuric acid and sodium nitrite. The cellulose was also separately exposed to a mixture of nitric oxide and nitrogen dioxide gases. After these gas exposures, the cellulose was treated in a way that allowed the researchers to extract any nicotine and by-products left on the cellulose.
What were the basic results?
The major compound identified when the smoke-absorbed cellulose was exposed to nitrous acid was NNA, a type of TSNA that is not normally present in freshly emitted tobacco smoke. Although this is not known to be a carcinogen, it has been demonstrated to cause mutations in a similar way to the carcinogen N-nitrosonornicotine (NNN). Low levels of NNN were also detected in the cellulose, along with another carcinogen called NNK.
The three TSNA compounds in the cellulose were formed at a fast rate, with maximum concentration in the first hour of exposure. When the cellulose was exposed to nitrous acid for three hours, there was a greater than tenfold increase in the amount of surface-bound TSNAs.
When the smoke-absorbed cellulose was exposed to nitric oxide and nitrogen dioxide only (without nitrous acid) the researchers detected only NNA and NNK.
How did the researchers interpret the results?
The researchers conclude that the chemical process identified represents “an unappreciated health hazard” given the rapid absorption and persistence of nicotine on indoor surfaces such as clothes and skin. Their findings raise concerns about exposures to tobacco smoke residue, which some have termed ‘third-hand smoke’.
This is important laboratory research that has demonstrated that new carcinogenic substances develop when a natural substance (cellulose) is exposed to nicotine, and then later exposed to a nitrous air mixture.
Although the compounds identified in this study could potentially be absorbed through the skin, inhaled or ingested, this preliminary research did not aim to answer important questions over how much residue a person would absorb in a real-life situation or the direct health effects of absorbing these substances. Nevertheless, this research justifies further study into the toxicity and cancer-causing properties of the main substances identified and an investigation into the way they are absorbed by humans. The researchers would also need to directly examine the levels of these toxic compounds found on exposed skin, hair, clothes, furnishings and other materials.
While it is not yet known how much danger might be posed by third-hand smoke, the dangers of being a smoker and secondhand smoke are well established. The best advice that can be given to smokers at this time is to be considerate of the health of others and smoke away from other people, outside or in a specially designated room. These types of measures are particularly relevant in the family home, where steps should be taken to ensure that babies or children are not exposed to cigarette smoke or its by-products.