The team hopes their findings will deter people from taking up smoking and debunk the myth that social smoking is harmless. Every cigarette has the potential to cause genetic mutations, Alexandrov says.
Quitting smoking will not reverse these mutations – they leave permanent scars on DNA – but it will prevent the added risk of more mutations
There is good evidence that people who stop smoking have a significantly lower risk of premature death than those who continue, says Simon Chapman at the University of Sydney, Australia.
For example, a UK study that followed 35,000 men for half a century found that smoking shaved 10 years off average life expectancy. But quitting at age 30 mostly erased the risk of premature death, and giving up at 50 halved it.