[Author's note: When I first wrote this article I had no idea how widespread is the notion than breathing secondhand smoke was more dangerous than smoking. Since putting the article online I have seen the traffic that has come to it by people searching under key words such as 'why is second hand smoke more dangerous than first hand smoke', 'second-hand smoke more dangerous than first-hand smoke', 'the reason second hand smoke is more dangerous than first hand', 'second hand smoking is worse than first because the particles are more concentrated' and 'why second hand smoke causes more harm than first hand'. That is just a very small sample.]
In the second of this series of articles looking at bizarre claims made by the anti-smoking movement, we shall see how the notion came about that secondhand smoke is more 'toxic' than firsthand smoke. As ridiculous as it is, this claim has recently gained considerable currency not only with anti-smoking groups but with the public and even with some politicians. No one individual is directly responsible for this myth arising and no published study has ever explicitly made the claim. Instead, the idea took hold because of a simple misunderstanding and was allowed to flourish because those who should know better had no desire to correct it.
What really started it off was a paper written by Stanton Glantz and Suzaynn Schick in 2005 for the Tobacco Control journal. Stanton Glantz is the high-priest of the anti-smoking movement and this is not the last time we shall encounter him in this series of articles. Having spent ten years studying mechanical engineering, Glantz abandonned the subject in 1973 to embark on a two year course in cardiology. In 1977, he was installed as an assistant professor of medicine at the University of California, San Francisco (1). With his bushy hair, spectacles and array of brightly coloured tee-shirts, Glantz looked every inch the nonconforming West Coast academic. In 1981, he co-founded Californians (later Americans) for Nonsmokers' Rights and set out on his long crusade to portray secondhand smoke as one of most dangerous poisons known to man.
The paper in question - 'Philip Morris toxicological experiments with fresh sidestream smoke: more toxic than mainstream smoke' - is actually perfectly sound for what it is: a straightforward review of a number of obscure experiments conducted by Philip Morris in the 1980s which came to light when the tobacco industry was forced to make its internal documents public in 1998.
The study discusses a series of experiments in which laboratory rats were exposed to very high levels of 'sidestream' and 'mainstream' smoke. Understanding the distinction between the two is crucial in what was to come. Sidestream smoke is, as Glantz correctly described it in the paper, "the smoke that rises from the tip of the burning cigarette between puffs" (2). Mainstream smoke is that which is inhaled and exhaled by the smoker. The definition of mainstream smoke is clumsy and muddled since there is a huge difference between inhaled and exhaled smoke. 1979 Surgeon General's report stated: "When the smoker inhales the mainstream smoke he exhales into the atmosphere less than one-seventh of the amount of volatile and particulate substances that were originally present in the smoke" (3). Exhaled smoke, then, is considerably less 'toxic' than either the smoke that comes from the burning tip or the smoke that is inhaled through the cigarette. That much has always been clear; but the Surgeon General also suggested that inhaled mainstream smoke might be also less toxic than sidestream smoke. It was this hypothesis that inspired the Philip Morris experiments, which began in 1981.
In a secret laboratory in West Germany, rats were placed in tight glass tubes and exposed to extreme concentrations of tobacco smoke on a daily basis. Some of the rats were forced to breathe mainstream smoke, others were given sidestream smoke. The only problem was that inhaled mainstream smoke is very difficult to reproduce and the scientists did so by using a very simple technique: they diluted it with air.
The diagram above was drawn by the scientists who conducted the experiments. The machine on the left is producing sidestream smoke from a smouldering cigarette. The machine on the right is producing mainstream smoke. Notice how the mainstream smoke is coming from the mouth-end of the cigarette and is going down a tube which is open at the top and bottom. This allows the smoke to be diluted by the air. If you look very carefully you can see the words 'dilution air' above it. Contrast that with the sidestream machine which is virtually sealed, thereby forcing concentrated tobacco smoke from the lit end into the tubes.
After three weeks, half the rats given the undiluted sidestream smoke had died; compared to just one from the mainstream smoke group. The hypothesis was proven: sidestream smoke was more toxic than mainstream smoke or, to put it more prosaically, the more smoke is filtered and diluted, the less toxic it becomes.
What could be learnt from this rather mundane and predictable finding? It told us nothing about passive smoking because the doses involved were thousands of times higher than would be inhaled by the heaviest smoker, let alone a passive nonsmoker. The rats that were given the 'sidestream' smoke were being practically asphyxiated with constant, pure tobacco smoke. The difference between the two was underlined by the temperature the rats endured: from a warm 25 degrees celsius in the mainstream smoke tubes to a decidedly toasty 34 degrees in the sidestream smoke tubes.
The scientists who conducted the experiments were well aware that they were not replicating real-life conditions, nor were they trying to. In their report, they stated the obvious:
It would be several years before Philip Morris scientists began exposing rats to anything approximating real secondhand smoke and when they did so it was with very different equipment. Ageing and diluting the smoke was the key. The apparatus from a typical passive smoking study is shown below.
Note the 'conditioning room' between the cigarettes and the rats and note, too, how much more ventilation has been provided. Even with this dramatically less confined arrangement, those who conducted the experiments estimated that the rats were still being exposed to 10 to 100 times more smoke than any nonsmoker would ever experience, even in the most extreme real life situations. Despite these high doses, which lasted 8 hours a day, every day for up to a year at a time, none of the rats died and there was little evidence of physical harm.
But it was the first set of experiments that were the focus of Glantz and Schick's 2005 paper. The authors used them to show that "whole fresh sidestream smoke is 2-6 times more toxic" than mainstream smoke. The key words in this sentence, however, are "whole" and "fresh"; they were clearly only talking about the smoke that comes off the cigarette at the moment of combustion and not the mixture of sidestream smoke, mainstream smoke and ambient air that makes up secondhand smoke.
Glantz and Schick did not show the diagrams that I have reproduced here, but it should be immediately clear to anyone who views them that the Philip Morris scientists were using a very specific definition of sidestream smoke which had, at best, only a theoretical relevance to real-life human conditions.
It is commonly said that secondhand smoke is 85% sidestream smoke and 15% mainstream smoke. This completely ignores the ambient air which dilutes it. How much it is diluted by depends on the size of the room and the level of ventilation. An article in Regulatory Toxicology & Pharmacology estimated that passive smokers inhale 1/10,000th to 1/100,000th of the respirable tobacco smoke that smokers do. Even if the true figure is as low as 1/1,000th, the real breakdown of what constitutes secondhand smoke would be 0.085% sidestream smoke, 0.015% mainstream smoke and 99.9% ambient air. Once the diluting effect of the air is taken into account, the subtle differences between sidestream and mainstream smoke become largely academic.
The relative toxicity of sidestream and mainstream smoke is, therefore, a red herring. No nonsmoker inhales pure sidestream smoke or anything close to it. They might inhale secondhand smoke but that only contains a tiny amount of sidestream - and exhaled mainstream - smoke which has aged, broken down, clung to surfaces and been greatly diluted before it gets anywhere near them. Many of the constituents of secondhand smoke that people have been taught to fear cannot even be detected in secondhand smoke, even with modern scientific apparatus. Less than 10% of the chemicals that are said to be in mainstream smoke have ever been identified in secondhand smoke (5).
The difference between breathing sidestream smoke and secondhand smoke is rather like the difference between sucking exhaust fumes from a car's tailpipe and standing by a road. You might be being exposed to the same chemicals but the outcome is going to be very different.
For anti-smoking groups, the vast rate of dilution goes unmentioned. Part of the confusion lies in the terminology. Anyone not well-versed in the science could be forgiven for assuming that sidestream smoke is just another word for secondhand smoke. That being the case, it was almost inevitable that anti-smoking activists - whose understanding of science can be shaky at the best of times - would allow their heart to rule their head and assume that passive smoking was more dangerous than smoking.
A look at some typical quotes from anti-smoking websites shows how complex laboratory experiments have been dumbed down for public consumption:
It would take a lawyer to decide if these statements can be described as technically accurate or not. Generally, anti-smoking groups are smart enough to limit their definition of mainstream smoke to mainstream exhaled smoke. When they do so, they are on safe ground. Smokers absorb most of the toxins in their bodies; consequently, what they breathe out is considerably less toxic than fresh smoke. This distinction, however, will go over the head of many readers, who will likely infer that breathing secondhand smoke is more dangerous than smoking itself.
And these are the more measured statements. There are plenty of other groups who have gone past suggestion and insinuation, and are now openly claiming that smoking is "worse" than smoking:
Once the anti-smoking groups adopted the idea, it was inevitable that the politicians they lobbied would succumb. State Rep. Peter J. Daley of Washington called for legislation to ban smoking in vehicles if one of the passengers was a child, saying:
And finally the idea took hold amongst the general population. The website Wiki Answers deals with the issue very succinctly:
A: Yes. Second hand smoking is more dangerous than first hand (13)
The myth of nonsmokers being in more danger than smokers is particularly prevalent on internet message boards, blogs and amongst young people in America and Canada who have been fed stories about passive smoking their whole lives. The net result is that secondhand smoke assumes the role of a supernaturally lethal gas and the wheels are greased for the passage of smoking bans. Those who might normally oppose a ban have been persuaded that passive smoking represents a peril too great to ignore. Take this typical quote from a resident of Scranton, Pennsylvania who, when a smoking ban was brought in, was said to be "thrilled":
In fairness to Glantz and Schick, their 2005 study did not claim that secondhand smoke was more toxic than firsthand smoke, only "fresh sidestream smoke". Nonetheless, Glantz is a shrewd operator who has publicly stated that he only does research if he believes it will help the anti-smoking cause (15). He must have known what he would unleash when he published the sidestream smoke study and, if not, he has certainly fanned the flames since.
What could be more ridiculous than saying that diluted smoke is more dangerous than concentrated smoke? How about saying that diluted smoke gets more dangerous as it gets older?
Step forward Stanton A. Glantz, who, in 2007, returned to the Philip Morris archive with a new article which made that very claim (also published in Tobacco Control). He did so by looking at the five Philip Morris passive smoking experiments mentioned earlier. These provided a wealth of information, even if it wasn't the kind of information anti-smoking groups wanted to hear. One of them, for example, found that "tumors [in the rats exposed to smoke] were similar in number to those seen in the sham-exposed groups." (16) Another reported that: "The test atmosphere had no effect on the general condition and behavior. During the inhalation period one rat died of a technical cause. No test atmosphere related mortality was observed." (17)
Glantz did not comment on the most notable outcome of the experiments - that heavy doses of secondhand smoke did not kill any of the rats - and actually disregarded three of the experiments completely. This left him with two passive smoking experiments, conducted in 1994 and 1997 (the apparatus shown in the second diagram above comes from the report of the 1997 experiment).
He compared these two secondhand smoke studies with the sidestream experiments of the early 1980s, paying particular attention to comments made by those who dissected the rats afterwards. He developed a points system of his own making which purported to measure the physical damage to the rats. These numbers were then entered into a convoluted mathematical equation, along with other data he gleaned or inferred from the written reports. When the calculations emerged from his computer something amazing happened: he was able to show that, pound for pound, the fresh sidestream smoke had caused less damage than the diluted secondhand smoke. Not only that, but the diluted secondhand smoke became more harmful as it got older (18).
This was entering the realms of madness. Half of the rats that had been given fresh sidestream smoke had died for goodness sake! It was hard to see how any more harm could have come to them. By contrast, none of the rats exposed to aged, diluted sidestream smoke had died.
Glantz admitted that he had no idea what "the mechanism for the increased toxicity of aged sidestream smoke" might be, although he seriously suggested that smoke particles absorbed in home furnishings could wait a while before springing back into the air to attack nonsmokers (19).
Glantz also accepted that earlier studies of sidestream smoke had shown "toxicity decreased rapidly in the first 30 seconds of aging." And he noted that, according to his mathematical equation, one experiment had shown that toxicity trebled with ageing and the other showed that it halved. Glantz described this as "remarkable." 'Magical' would have been a better word; the two findings were completely at odds with one another.
If the fact that his hypothesis went against existing toxicological principles was not enough to make Glantz question his own methodology then his own conflicting data should have been. And these were not the only flaws. The experiments Glantz re-examined were conducted years apart, by different scientists, with different apparatus and were designed to study completely different things. The collected reports for these experiments runs to many hundreds of pages, but in none of them is there any suggestion sidestream smoke becomes more toxic with age. In fact, when the results of one of the experiments were published in Toxicological Science in 1998, the authors concluded that the opposite was true:
Not a man crippled by self-doubt, Stanton Glantz ignored all the evidence that he might be wrong and pushed on with his hypothesis:
And there you have it. Sidestream smoke is TWELVE times more deadly than mainstream smoke! So if you're worried about secondhand smoke, make sure you get close to the burning cigarette so it doesn't get too old. If you really want to play it safe, smoke the cigarette yourself.*
* Not really
See http://www.velvetgloveironfist.com/index.php?page_id=38 for references.