Is “Thirdhand Tobacco Smoke” a Valid Scientific Concept or a Public Relations Gimmick? — A Post from Geoffrey Kabat

Geoffrey Kabat is the author of Hyping Health Risks: Environmental Hazards in Daily Life and the Science of Epidemiology.

“There are enough scientifically documented harmful effects of exposure to cigarette smoke without concocting catchy but uninformative concepts that, while likely to attract the attention of the jaded media and its audiences, confuse the important issues regarding the health effects from exposure to cigarette smoke.”—Geoffrey Kabat

Hyping Health RisksThe current issue of the journal Pediatrics (January, 2009) carries an article titled “Beliefs about the Health Effects of ‘Thirdhand’ Smoke and Home Smoking Bans”. The study has been reported by the New York Times, the BBC News, and many other news outlets.

The authors of the article, tobacco researchers from Harvard and several other institutions, defined “thirdhand” smoke—in contrast to the better-known secondhand smoke—as the “residual tobacco smoke contamination that remains after the cigarette is extinguished.” They characterized secondhand smoke as the smoke that is visible while the cigarette is being smoked.

Having defined this “novel” exposure, the researchers conducted a survey to determine whether respondents thought that exposure to thirdhand smoke was harmful for children compared to secondhand smoke. Their results indicated that the vast majority of respondents (both smokers and nonsmokers) believed that secondhand smoke harms the health of children, and that smaller but still sizeable proportions of smokers and nonsmokers believed that thirdhand smoke harms children.

The authors conclude that educating parents about the hazard of thirdhand smoke may contribute to making homes smoke-free. (The home is the principal remaining venue where smokers can freely exercise their habit). Few people in public health would quarrel with this objective.

However, since the article presents itself as science (with representative samples, multivariable analysis, statistical tests, and references to the literature), it is fair game to look at the validity of their concepts and inferences.

The authors’ distinction between secondhand and thirdhand smoke is artificial and betrays an ignorance of the relevant science. The preferred term used in studies of nonsmokers’ exposure to the cigarette smoke of others is “environmental tobacco smoke,” or ETS. ETS consists of a mixture of sidestream smoke emitted by the burning tip of the cigarette and the smoke exhaled by the smoker. Over time the smoke is diluted, ages, and gets deposited on surfaces.

I asked Roger Jenkins, an analytical chemist who has done extensive work on exposure to ETS and has written a major textbook on the topic, what he thought about the concept of “thirdhand smoke.” He made the following points: “ETS is made up of two phases, the vapor phase and the particulate phase. Secondhand smoke is NOT the stuff you see, and “thirdhand smoke” is NOT the stuff you don’t see. If someone wants to use the term secondhand smoke, he must acknowledge that it contains BOTH the stuff you see (particles) and the stuff you can’t see (vapors and gases).”

What is most relevant for human health is the total quantity of smoke a nonsmoker is exposed to while in the home. For this reason, studies of exposure to ETS make use of the average airborne concentration of markers of tobacco smoke, such as airborne nicotine, or other compounds in tobacco smoke, and/or markers of actual exposure, such as 24-hour urinary cotinine (a breakdown product of nicotine).

Since the distinction between secondhand and thirdhand smoke is an artificial one, questioning study subjects about their beliefs concerning the dangers of thirdhand smoke is questionable.

In the opening sentence of their abstract, the authors state that “there is no safe level of exposure to tobacco smoke.” While there are different theoretical models regarding effects of exposure at low levels on carcinogenesis, in practice there are levels below which any effects are likely to be trivial or undetectable. In fact, the dose does matter. Apart from the degree of ventilation, humidity, room size, and other characteristics of the home, the single greatest determinant of exposure is likely to be the number of cigarettes smoked in proximity to children.

One aspect of the study that appears valid is the researchers’ implied reference to toddlers, who are likely to ingest some amount of tobacco smoke constituents deposited on floors and other surfaces. If the authors had focused on this special case in order to educate the parents of newborn children about the hazards of smoking, this would have been a better-conceived project.

The special case of toddlers is yet another reason for parents not to smoke in the home, in addition to the greater susceptibility of infants and children to the adverse effects of smoke exposure, the fact that unextinguished cigarettes can cause fatal fires, and the vitally important fact that parental smoking has a strong influence on whether or not children grow up to become smokers themselves.

There are enough scientifically documented harmful effects of exposure to cigarette smoke without concocting catchy but uninformative concepts that, while likely to attract the attention of the jaded media and its audiences, confuse the important issues regarding the health effects from exposure to cigarette smoke.

3 Responses

  1. Interesting. Columbia University Press has left up a two-liner piece of advertising spam clickbait for its readers here of the last four years. But at the same time they deleted (or refused to accept) my somewhat more relevant scientific analysis of Dr. Kabat’s writing and the original research. On the off-chance that the deletion was unintentional, I’ll paste it here again from my files:


    Dr. Kabat is largely correct in his analysis of the distinction between “secondhand smoke” (which is the term preferred by antismoking activists over the more descriptive ETS since it implies the concept of smoke that has been “used” and then foisted upon innocents as it is being thrown away) and “thirdhand smoke” (which variously can be used to describe exposure to the smoke particles left deposited as smoke settles from the air or to smoke components sublimating into the air after such deposition). I feel he fails in properly emphasizing the importance of the varying extent of such exposures however, and in comparing those extents to the exposures experienced by smokers themselves. He also makes little mention of the degree to which such minute exposures have been blown out of proportion by the media with the seemingly willing abetment of the researchers through their statements, or of the damage caused by this.

    Let me take one particularly important and egregious example: the January 2nd New York Times article on this research. The article reserves the spotlight closing paragraph of the article to provide the obligatory listing of nasty things found in standard cigarette smoke along with descriptive phraseology (e.g. “hydrogen cyanide, found in chemical weapons; butane, which is used in lighter fluid”). It finishes with one element particularly designed to terrorize parents in today’s world, “polonium-210 (Po210), the highly radioactive carcinogen that was used to murder former Russian spy Alexander V. Litvinenko in 2006.”

    After reading such an article, what decent parent would allow smoking in their home, even if their children were not present. To go beyond that, what decent parent would even allow their children to associate with children of known smokers or allow smoking granny to stop in for Christmas and irradiate their children with the offgassing of KGB murder weapons? The claims, if true, would go far beyond reducing simple in-home smoking, they would drive deep and destructive wedges into our fundamental social fabric.
    Still, if true, perhaps the damage would be worth it. But are they true? Or are they the modern equivalent of the “yellow journalism” that has driven our society to irrational actions and even war in times past? I believe the latter is the truth. Since the Times chose to emphasize it in such scary terms, let’s take a look at this KGB killer highlighted in their story, the radioactive Po210.
    Some elementary research tells us that the Russian was murdered by a dose thought to be about 5 millicuries while a smoker smoking a half pack of cigarettes per day ingests roughly a half picocurie of this element. At typical nonsmoker living or working would likely get roughly a hundredth of the smoker’s dose, or about 5 femtocuries per day. A millicurie is a thousand microcuries, a million nanocuries, a billion picocuries, or a trillion femtocuries.

    It would take that nonsmoker a trillion days to absorb the dose that killed the Russian.

    Of course that’s secondhand smoke. What about our children and this “third-hand smoke”? A reasonable estimate for the amount remaining stuck to the 10,000 square feet of walls, ceilings, furniture, floors, and draperies in a reasonably ventilated 2,000+ square foot home would almost certainly be less than 1%, but let’s assume that 1% actually does remain and spreads out over that 10,000 square feet of surface. With ten cigarettes having been smoked while the child was at school and the house then thoroughly aired out, we’d then have 1% of a half picocurie (i.e. 5 femtocuries) spread over that surface.

    Let us suppose that your child has a “floor-licking fixation” and licks an entire 10 sqare feet of floor sparkly clean every day while your back is turned. That child will then have licked 1/1,000th of those 5 femtocuries into his system: 5 “attocuries.”

    So, how long would it take such a child to get the “killing dose” of the murdered Russian featured in the Times?

    In 1,000 days your child would have licked up 5 femtocuries.
    In one million days, 5 picocuries.
    In one billion days, 5 nanocuries.
    In one trillion days, 5 microcuries.

    It would take one quadrillion days (2.74 trillion years) for that child to absorb 5 millicuries.

    Unfortunately the universe is only 10 billion years old, so the child would have to lick floors for 274 times as long as our entire universe has existed to match the dose our poor radioactive Russian receieved that merited the NY Times coverage.

    Of course since he’d normally excrete most of that polonium we’d have to refuse to change his diaper until the end of that period… not a very pleasant thought.

    And then there’s that whole annoying fact that the half life of polonium is only 138 days, so we’d just have to ignore the laws of physics as well in justifying the Times’ comparison.

    Even if someone wanted to quibble with these estimates, changing 1% to 10%, or 10 square feet to 100, or 10 cigarettes to 100 cigarettes per day… or even ALL THREE in attacking this argument… we’d STILL be talking three billion years of exposure along with a suspension of the basic laws of biology and physics.
    Other elements in “third-hand smoke” might be somewhat more concentrated, but still nothing that wouldn’t demand hundred, thousands, or millions of years of assiduous tongue-licking and total constipation.

    Dr. Kabat’s central point, the undesirability of confusing the science around smoking with the almost superstitious concern about such nonsensical concepts as “third-hand smoke” is valid, but he doesn’t go far enough in condemning either the gullible headline-seeking media or in recognizing the degree of harm caused by researchers whose agenda is driven more by politics than by science.

    Michael J. McFadden
    Author of “Dissecting Antismokers’ Brains” (2003) and “TobakkoNacht — The Antismoking Endgame” (2013)

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