People who smoke low-tar cigarettes are just as likely to develop lung cancer as other smokers, doctors have warned.
Smokers are advised to quit rather than switch to 'mild' brands
Researchers in the United States examined data on more than 900,000 people, many of whom smoked.
They found that people who smoked very low or low tar cigarettes had similar rates of cancer as those who smoked stronger brands.
Writing in the British Medical Journal, they said the study is more evidence that all cigarettes harm health.
A number of studies have shown that people who smoke low tar cigarettes are still at risk of developing lung cancer.
However, there is strong evidence to suggest that this message is not getting through to smokers.
A survey of 780 British women who smoked so-called "mild" cigarettes, published in 2001, found two out of five thought they were doing themselves less damage than if they smoked stronger brands.
Last year, Cancer Research UK launched a major advertising campaign warning smokers not to be fooled into thinking low tar or mild cigarette brands are less harmful.
In this latest study, doctors from Massachusetts General Hospital and the American Cancer Society examined the records of 364,239 men and 576,535 women who had signed up to take part in a major cancer prevention study in the 1980s.
Over 78,000 men and almost 113,000 women smoked cigarettes in 1982.
Of these, some 8% of men and 14% of women smoked "very low tar" brands - less than 7mg of tar.
Another 35% of men and 43% of women smoked "low tar" brands - between 8mg and 14mg of tar.
The researchers compared lung cancer rates in these groups with those of other smokers.
"Men and women who smoked very low and low tar brands had risks of lung cancer indistinguishable from those who smoked medium tar brands," the researchers wrote.
The study found that people who smoked non-filter cigarettes with 22mg or more of tar were most likely to develop lung cancer.
However, it also backed up other studies which have suggested that people who stop smoking in their early 30s can reduce their risks of lung cancer substantially.
"People who quit smoking before age 35 years had risks of lung cancer approaching those of people who had never smoked," they said.
Professor Martin Jarvis of Cancer Research UK welcomed the study.
"This study provides convincing evidence to back up Cancer Research UK's recent advertising campaign showing how smokers are misled by tobacco companies into thinking that low tar or 'light' and 'mild' cigarettes are less dangerous.
"Choosing to smoke low tar cigarettes does not result in a lower risk of lung cancer. Low tar cigarettes offer smokers a false promise of reduced risk," he said.
"The only effective way for a smoker to reduce risk is to quit, as this study once again confirms."