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Thirdhand smoke fever - another example of prejudice and propaganda

Friday February 12, 2010

Chris Snowdon, author of Velvet Glove Iron Fist: A History of Anti-Smoking, explains the “science” behind the latest anti-smoking scaremongering

It was the kind of laboratory experiment that two chemists might conduct to kill time on a rainy Friday afternoon. It resulted in global media coverage. The Daily Telegraph was only marginally more excitable than the many other newspapers which reported it:

“Third-hand smoke as dangerous as cigarette fumes … Third-hand smoke found in hair and on clothes can be as dangerous as the fumes billowing directly from a cigarette – particularly to babies and children.”

This came just over a year after the concept of ‘thirdhand smoke’ – toxins lingering in hair and furniture for months after a cigarette is extinguished – was first launched into the public consciousness. On that occasion, a telephone survey asking whether parents would be less likely to smoke if they believed that dormant carcinogens in the upholstery could attack their children was reported as if such a phenomenon had already been proven. In fact it had not even been studied, but this speculative survey was enough to prompt think-of-the-children hyperbole from the Daily Mail under the headline: ‘Even smoking outside can harm your baby’.


Having established that a section of the public was open to the idea of a new health scare, the first laboratory experiment was commissioned (the order of events providing an insight into how these things work). Conducted in the respected Lawrence Berkeley National Laboratory in California, this experiment involved putting nitrous acid in contact with nicotine to see if the reaction created tobacco-specific nitrosamines (TSNAs). Specifically, they were looking for NNA and two known carcinogens – NNN and NNK.

The nicotine had been absorbed into a surface, hence ‘thirdhand smoke’, although not the clothes and hair mentioned in subsequent news reports. Instead, the glove compartment of a truck driven by a heavy smoker was selected; the smallest and most confined workplace imaginable. A sample was taken by wiping the glove box and the nitrous acid was then sprayed on, with underwhelming results. No NNN was found and both NNA and NNK were found at barely detectable levels, both under 1 ngcm-2. This was the closest the researchers came to experimenting in real-life conditions.


In a further experiment, the team collected a sample from the truck using cellulose substrates which absorbed twice as much nicotine and, unsurprisingly, yielded twice as many TSNAs, albeit still well below 5 ngcm-2. They then exposed some cellulose substrates to secondhand smoke, but the levels of TSNA produced were, as the authors reported, “negligible”. Finally, they gave up using cigarettes altogether and simply impregnated the cellulose substrates with pure nicotine vapour. This produced nicotine concentrations that were 15 times higher than were found in the truck and when the nitrous acid was applied, the researchers were rewarded with a more newsworthy finding. Much higher levels of NNA were recorded (over 20 ngcm-2) and NNK also rose, albeit to a fairly feeble 3 ngcm-2.

Taken as a whole, this was remarkably flimsy evidence upon which to hang the claim that stale tobacco in clothes and furniture was “as dangerous as cigarette fumes”. Having come up empty-handed using a real-life smoking environment, the researchers had resorted to using nicotine vapour on cellulose substrates in an experiment that could not be replicated outside of a laboratory. Even then, they had not found NNN in any of the experiments and the only TSNA to appear in any quantity was NNA. This posed a problem because NNA doesn’t actually cause cancer, as the authors admit:

“NNA carcinogenicity has not been reported.”

This left them with one carcinogen that was barely present, one carcinogen that wasn’t present at all and one TSNA that was present but wasn’t a carcinogen. But even these inauspicious findings only hinted at a more fundamental problem with the study.


The paper had shown that nitrous acid molecules will react with absorbed nicotine (just as it would with free-floating nicotine) to produce TSNAs. The more nitrous acid in the room, and the more nicotine on the surface, the more the reaction will occur. But for the experiment to have any meaning beyond the walls of a Berkeley science lab, it needed to have some relevance to everyday life. People do not tend to spray their homes with nitrous acid. Was there, indeed, any reason for using nitrous acid at all, beyond the probability that it would create some nasty sounding chemicals?

Nitrous acid concentrations in the average Californian home are 4.6 parts per billion. The Berkeley researchers used concentrations of 65 parts per billion. They described this dose as “high but reasonable”, a baffling description since it is 14 times higher than would be found in a normal domestic setting. Since they were already using 15 times more nicotine than would be found in a smoky truck cabin, any relevance the experiment had to real life had long-since vanished. The concentrations were fantastically high when compared to the average home.


In any case, if your house or car is full of nitrous acid then you have more to worry about than it reacting with absorbed nicotine. As the authors point out in the study:

“The main indoor sources of HONO [nitrous acid] are direct emissions from unvented combustion appliances, smoking, and surface conversion of NO2 and NO.”

NO2 and NO themselves are products of unregulated combustion. So you’ll only be exposed to high concentrations of nitrous acid if you’re exposed to the products of combustion – ie you’re a peasant in a smoke-filled hut, you live in a very polluted city like New Delhi, or you are in fact smoking a cigarette. The combustion products themselves are carcinogens, and are present in much higher concentrations than the TSNAs. Your problem would be the nitrous acid, not the chair you smoked a cigar in last Christmas.

Chris Snowdon is author of Velvet Glove Iron Fist: A History of Anti-Smoking

Velvet Glove Iron Fist

Velvet Glove Iron Fist

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