"Mind if I smoke?" asks a nattily dressed man on a California billboard.
"Care if I die?" replies the woman standing next to him.
The billboard, sponsored by the California Department of Health Services, reflects the emerging conventional wisdom about secondhand smoke: It's so hazardous that smoking a cigarette near someone is tantamount to assault with a deadly weapon. Tobacco's opponents hope that impression, so useful in ostracizing smokers and encouraging them to quit, will be reinforced by this month's settlement of a class action lawsuit claiming injuries from secondhand smoke.
To resolve Broin v. Philip Morris, the tobacco companies agreed to pay $300 million for research on smoking-related diseases. The plaintiffs' attorneys got a breathtaking $49 million. But the plaintiffs, a group of flight attendants, got nothing, and the tobacco companies did not acknowledge any risk from secondhand smoke.
For decades, of course, these same companies refused to concede that smoking itself was dangerous. So it's hard to believe them when they express doubts about the hazards of secondhand smoke. Yet these doubts are shared by a number of reputable scientists, who argue that tobacco's opponents have exaggerated both the strength of the evidence against secondhand smoke and the level of risk involved.
"I just think a great deal more skepticism is in order," says Geoffrey Kabat, an epidemiologist at the State University of New York, Stony Brook, who served on the advisory panel that reviewed the Environmental Protection Agency's 1993 report on secondhand smoke. "If these were data on something else–risk factors for ingrown toenails or something like that–people would look at it and say, 'Well, it's really not too impressive….There's not that much there.' "
The uncertainty about the relationship between secondhand smoke and diseases such as lung cancer and heart disease stems mainly from the difficulty of determining whether an environmental agent has an effect at very low doses. Compared to smokers, people exposed to secondhand smoke absorb tiny amounts of the chemicals produced by tobacco combustion. "There is an enormous leap of faith to think that we know anything about the smoke way down there," says Michael Gough, a molecular biologist who worked at the U.S. Office of Technology Assessment for more than a decade and is now director of science and risk studies at the Cato Institute.
With low-level exposure, statistically significant results–findings strong enough to say with confidence that they did not occur by chance–are elusive. And even when researchers find that exposure to a particular substance is associated with a statistically significant increase in risk, the increase is likely to be small, making it difficult or impossible to rule out other causes.
"The noise is going to be bigger than the signal in that area," says UCLA epidemiologist James Enstrom. "You may never be able to resolve it." Gough agrees: "If environmental tobacco smoke causes cancer, I'm convinced we'll never show it. It's just beneath the level of detection." And Howard E. Rockette, a University of Pittsburgh biostatistician who served on the EPA's advisory panel, writes that "simple arguments in regard to statistical power, model dependence of extrapolation, and the potential for confounding when estimating low risks make this, as well as other low-dose problems, unsolvable using current techniques."
Official pronouncements about secondhand smoke gloss over the limitations of the evidence. Official propaganda goes a step further, implying that a small increase in risk among people intensely exposed to secondhand smoke for decades somehow translates into grave danger for people who stand next to smokers on the street or eat near them in restaurants. Even Harvard epidemiologist Dimitrios Trichopoulos, one of the first researchers to argue that prolonged exposure to secondhand smoke can cause lung cancer, concedes "there is an exaggeration" in public perceptions of the risk.
Richard Kluger, in his Pulitzer Prize-winning history of the tobacco industry, observes that "the government's agencies seemed nearly as capable…of blowing smoke at the public to cloud the scarcity of cold, clinical science in support of the indictment of [secondhand smoke] as a substantial public-health risk as the cigarette companies had habitually been in denying and distorting the overwhelming scientific case against direct use of their product." In the pursuit of a smoke-free society, as in the pursuit of tobacco profits, truth is expendable.