Michael Mosley investigates the dramatic rise in e-cigarettes. They're everywhere these days, but what does the latest scientific research on them reveal? Michael reveals what e-cigarettes are really doing to your health. Are they really better for you than cigarettes? What is actually in them? Is passive vapour harmful? And can they really stop you from smoking? Michael meets some of the scientists around the world studying them, asks a group of volunteers to try to give up smoking regular cigarettes using them, and even takes up 'vaping' himself, smoking an e-cigarette every day for a month to see the effects on his own health - no easy task for such a committed non-smoker.