Apparently, this is a tradition that spread across Europe during the bad old days of the Bubonic Plague. Between 1665 and 1667, The Bills of Mortality listed 68,576 plague victims in London alone (The true figure is believed to be closer to 100,000). But this was nothing compared to the Black Death pandemic that killed nearly one third of Europe's population (20 million people) in the 1300s.
Bubonic Plague was a horrible way to die. The victim's skin turned black in patches and inflamed glands (buboes – hence ‘bubonic’) grew in the groin. There was vomiting, splitting headaches and, in the pneumonic version of the illness, swollen tongues and throats, coughing and rheumy eyes. It must have been agonising. Because people believed that smells (known as miasmas) were the carriers of disease, they attempted to ward off the illness by dousing themselves in perfume or by holding a posy, or nosegay, of flowers to the nose.
But back to this ‘Bless you’ business. There is a story that, during the Great Plague, Pope Alexander VII (1599-1667) passed a law requiring people to bless anyone who sneezed. At the same time, the sneezer was expected to cover their mouth with their hand or a cloth. This was to stop the spread of the illness. However, I can find no validity to this story. It may be a variant of a similar story involving Pope Gregory the Great (540-604) who became Pope when his predecessor died of plague. Gregory therefore called for unceasing prayer for God's help and that when someone sneezed, they were to be immediately blessed in the hope that they would not develop the plague. But the tradition is even older than that. Although the origins are obscure, it is mentioned in texts as long ago as 77AD when the somewhat barmy Pliny the Elder recorded in his Natural History:
‘Why is it that we salute a person when he sneezes, an observation which Tiberius Caesar, they say, the most unsociable of men, as we all know, used to exact, when riding in his chariot even?’
Incidentally, this may be related to the old superstition about holding your breath while passing a cemetery. The idea is that you will not then inhale any evil spirits that are lurking about. It is perhaps no coincidence that in almost all languages, the word for "soul" usually derives from the word for "breath", "wind", "air" etc.
I can’t believe there’s so much superstition around such a mundane activity as sneezing. I found this rhyme today:
Sneeze on Monday for health,
*Gregory Y. Titelman - Random House, New York, 1996.