Gesundheit is the German word for health. When somebody sneezes, Germans often say "Gesundheit!" to wish them good health. This expression has found its way into the English language with the first recorded examples appearing in the 1910s. The expression was probably common even earlier in German speaking areas of America and spread outwards from there.

There are different theories about the origin of this phrase. One explanation is that the expression stems from the Middle Ages when the Bubonic Plague and other diseases were threatening Europe. In this case the one saying "Gesundheit" was actually wishing for good health for himself and trying not to catch anything from the one who had sneezed. Another superstitious explanation is that it was a belief that sneezing opened up an area in one's body through which evil spirits could enter. Saying gesundheit was a form of a blessing with which to keep out demons while the body was defenseless.

Superstitions date back as early as Ancient Greece (ref. Herodotus, "History" 440BCE). The soul was thought to leave the body through the nose upon death, so a powerful sneeze was thus considered a somewhat ominous or portentious event.

There is also a story that in the United States, legislation passed during World War I making it illegal to say "Gesundheit" has not been repealed up to the present day. So, technically speaking, you are committing an offence if you say "Gesundheit" to someone who sneezes. The whole thing is of course a fabrication, but nevertheless an amusing one!