I love the Naked Scientists site – they explain things so well. And snot is always interesting.
The average sneeze can propel a mucus missile and its microbial passengers at up to 100 miles per hour, hence the saying “coughs and sneezes spread diseases”, and as well as sneezing there is of course nose blowing. But much to the disgust of many a reader, the vast majority of our mucus is in fact eaten! Our airways are lined with millions of tiny hairs, called cilia. These beat in synchrony to produce waves of movement, a bit like how a Mexican wave moves around a football stadium. These waves sweep the mucus to the back of the throat where it is swallowed. Stomach acid then takes care of most of the things inside that could be infectious. But if the mucus dries out and hardens before it can be ferried to the throat it can produce an unsightly bogey!