The word 'smog' has been around since the early 20th century and was shorthand for 'smoky fog'. The first smog was recorded in London in 1873. These original smogs came from industrial pollution, such as burning coal. Today's smog is more likely to be caused by vehicle exhausts in places where smoky factories are a thing of the past. But in the developing world, industry as well as traffic, may result in the creation of smog. Whatever the cause, smog is a significant health risk to those exposed to it.