The reason is a phenomenon known as compensation. Most smokers are hooked on nicotine and crave a certain daily dose. If a light cigarette gives them too small a dose in each puff, they will make up the difference, often unconsciously, by taking more puffs, inhaling more deeply, covering cigarette ventilation holes or simply smoking more cigarettes. More than 95 percent of all smokers compensate, with many replacing every bit of tar and nicotine they thought they were avoiding.

 The tobacco industry has known about this phenomenon since at least the late 1960’s, as revealed by internal company documents cited in a recent decision by a federal judge in the District of Columbia. But it is distressing to learn how easily the companies fooled public health experts and federal regulators. The Federal Trade Commission adopted a method to test cigarettes on a smoking machine that would measure the amount of tar and nicotine, and a 1981 Surgeon General’s report even suggested that smokers unable to quit would be well advised to switch to cigarettes that scored better on the test. Unfortunately, a cigarette could look a lot safer when smoked by the machine than when smoked by nicotine-addicted humans.

 No wonder there has been no decline in the risk of lung cancer or other smoking-related diseases even though smokers have moved in droves to supposedly safer cigarettes. Smokers of light or low-tar cigarettes need to realize that the industry is not so much concerned about their health as it is worried, in the words of an internal document, that their penchant to quit smoking entirely could pose "a special problem for the cigarette industry."