Ask The Doctors

DEAR DOCTOR: I smoked cigarettes for years, but I always used the filtered kind. (I've since stopped.) Now I'm hearing that people who smoke filtered cigarettes have increased rates of lung cancer compared to those who smoke unfiltered cigarettes. How can this be?

DEAR READER: First of all, let me congratulate you for kicking the habit. No doubt it was hard, but giving up smoking was the best thing you could have done for your health. By doing so, you decreased not only your risk of lung cancer and emphysema, but also your risk of a heart attack and vascular disease.

That said, I agree; at first glance, it doesn't make sense that filtering the tar from cigarette smoke can increase the risk of lung cancer. The cigarette industry, knowing the health risks of smoking tobacco, invented the filtration system in the 1950s specifically to reduce smoking-related injury to the lungs. In the late 1960s, only 7 percent of cigarettes had a filtering system, but by 1982, nearly 100 percent of cigarettes had a filtering device.

Prior to unfiltered cigarettes, the majority of lung cancers were squamous cell cancers. Because smokers at the time were predominantly male, these cancers were largely found in men. As filtered cigarettes became the predominant cigarette on the market, the rates of another type of lung cancer, adenocarcinoma, began to increase. During this same time period, women began smoking at greater rates, and these cancers were often the predominant type among female smokers.

In fact, rates of lung cancer in women have consistently been increasing since the 1970s, and the majority of these cancers have been adenocarcinomas. Further, while the overall rate of lung cancer in men has decreased over the last 40 years, the percentage of men with adenocarcinoma has increased.

Those facts establish a correlation between filtered cigarettes and adenocarcinoma of the lung. But a direct connection is less clear. After all, filtered cigarettes do substantially reduce the amount of inhaled tar. In 1954, a cigarette delivered 38 milligrams of tar; in 1997, it delivered 12 milligrams of tar. Cigarette companies even advertised the fact that filtered cigarettes delivered less tar, calling them "light" or "ultralight" cigarettes. That sounds good, doesn't it?

Note, however, that the filters themselves can lead smokers to take bigger inhalations to overcome the filters. Thus, they inhale more of the toxic substances and cancer-causing materials in the cigarettes. Additionally, filtered cigarettes burn more slowly, leading to more puffs per cigarette and the inhalation of more toxic substances. Also, without the high heat of unfiltered cigarettes, toxic substances are less likely to burn off. And finally, a cigarette filter -- based on where it sits upon a person's lips -- leads to increased water content within the filter, which enables toxic particles to move more easily into the lungs.

All these factors mean that toxic chemicals, such as nitrosamines and NNK, which have been linked to lung adenocarcinomas, are more likely to travel deeper within the lungs of people smoking filtered cigarettes than those smoking unfiltered cigarettes. Research has not yet proved that filtered cigarettes lead to higher rates of adenocarcinoma, but the Surgeon General's 2014 report suggested that cigarette design changes in the 1950s may indeed have led to the rise in adenocarcinomas of the lung.

Ultimately, the fact remains that cigarettes are extremely addictive -- and filters don't change that fact. With or without filters, cigarettes cause lung cancer. So the best course of action is to stop smoking (or to never start) and to not believe that a filter will decrease your risk of lung cancer.

Robert Ashley, M.D., is an internist and assistant professor of medicine at the University of California, Los Angeles.

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