Smoking tobacco is the single most dangerous voluntary activity in the world. It kills six million people a year, and if current trends continue that figure is expected to rise to 8 million people by 2030. Even if it does not kill you, it will give you bad breath, bad skin and cost you money. So why do so many of us still smoke?

(Photo: A man holds a cigarette over an ashtray. Credit: Patrik Stollarz/AFP/Getty Images)