“No safe level,” continued…

The idea that there is “no safe level of exposure to secondhand smoke” has to be one of the most misleading statements in public health. I mentioned it in a story about campus smoking bans yesterday. It pops up again today in a blog post about airport smoking areas at The New York Times by Nicholas Bakalar:

Five large-hub airports in the United States have designated indoor smoking areas. According to a study from the Centers for Disease Control and Prevention, they all have unhealthy air — even in places where no one smokes. […]

The researchers found that the pollution level in smoking areas of the five airports was 23 times as high as the level in nonsmoking airports, and the average in adjacent areas was five times as high.

The study, in the Nov. 20 issue of the Morbidity and Mortality Weekly Report, notes that no level of secondhand smoke exposure is safe, and even brief exposures can have adverse cardiovascular and respiratory effects.

Notice how much work the “no safe level” line is doing here. It allows the researchers to abdicate responsibility for showing that levels of particulate matter in the air surrounding smoking lounges are causing any actual harm. They have no need to relate this minuscule level of exposure to a level of risk — because, in fact, doing so is likely beyond epidemiology when the risks are this small, if they exist at all. As Jacob Sullum noted in 2006 when Richard Carmona’s Surgeon General’s report came out, the science in the report is much more modest than the “no safe level” hype that accompanied it:

Since it is difficult even to measure the health consequences of long-term, relatively intense exposure to secondhand smoke among people living with smokers for decades, how could one possibly demonstrate an effect from, say, a few molecules? It’s clear that the vast majority of people exposed to secondhand smoke suffer no noticeable injury, so in what sense is their exposure unsafe? “No safe level” is an article of faith, not a scientific statement.

And yet, unfortunately, the “no safe level” idea continues to be used as an easy shortcut by researchers — and then dutifully transcribed by health reporters.