According to Surgeon General Richard Carmona, secondhand smoke is so dangerous that you'd be better off if you stopped going to smoky bars and started smoking instead. "Even brief exposure to secondhand smoke," claims the press release that accompanied his new report on the subject, "has immediate adverse effects on the cardiovascular system and increases risk for heart disease and lung cancer."
Among smokers, these diseases take many years to develop. So if you got your health tips from the surgeon general, you'd start smoking a pack a day as a protective measure.
But you may want to look elsewhere for medical advice. Carmona is so intent on promoting smoking bans—a key element of the government's campaign to reduce cigarette consumption—that he absurdly exaggerates the hazards of secondhand smoke, hoping to generate enough public alarm to banish smokers from every location outside the home.
As the report itself makes clear, there is no evidence that brief, transient exposure to secondhand smoke has any effect on your chance of developing heart disease or lung cancer. The studies that link secondhand smoke to these illnesses involve intense, long-term exposure, typically among people who have lived with smokers for decades.
Even in these studies, it's difficult to demonstrate an effect, precisely because the doses of toxins and carcinogens bystanders passively absorb are much smaller than the doses absorbed by smokers, probably amounting to a fraction of a cigarette a day. Not surprisingly, the epidemiological studies cited by the surgeon general's report find that the increases in lung cancer and heart disease risks associated with long-term exposure to secondhand smoke are small, on the order of 20 to 30 percent. Among smokers, by contrast, the risk of heart disease is between 100 and 300 percent higher, while the risk of lung cancer is about 900 percent higher.
Because the associations found in the secondhand smoke studies are so weak, it's impossible to rule out alternative explanations, such as unreported smoking or other lifestyle variables that independently raise disease risks. Although the surgeon general's report concludes such factors are unlikely to entirely account for the observed associations, the truth is we don't know for sure and probably never well, given the limitations of epidemiology and the difficulty of measuring low-level risks.
Reasonable people can disagree about the meaning of these ambiguous data, and it's not surprising that supporters of smoking bans like Carmona are inclined to see a clear causal relationship, while opponents (like me) are inclined to be more skeptical. But there is no excuse for the kind of scare mongering in which Carmona engaged when he implied that you could drop dead from the slightest whiff of tobacco smoke.
Even supporters of smoking bans, such as longtime anti-smoking activist Michael Siegel, faulted Carmona for gilding the lily (blackening the lung?) by saying things such as, "There is NO risk-free level of secondhand smoke exposure." This position contradicts the basic toxicological principle that the dose makes the poison. Since it's hard to measure even the health consequences of heavy, long-term exposure to secondhand smoke, how could one possibly demonstrate an effect from, say, a few molecules? "No risk-free level" is an article of faith, not a scientific statement.
Speaking of which, Carmona was at pains to say he was merely summarizing the science, not making policy recommendations, even though he emphasized that smoking bans are the only way to eliminate the "serious public health hazard" posed by secondhand smoke. He is right about this much: The issue of what the government should do about secondhand smoke is independent from the issue of exactly how risky it is. Whether smoking bans are a good idea is a question not of science but of values, of whether we want to live in a country where a majority forcibly imposes its preferences on everyone else or one where there is room for choice and diversity.