Why do we say, "God bless you" when someone sneezes?

Why do we say, "God bless you" when someone sneezes?: "Interesting, but the most popular theory comes from the Middle Ages. During the bubonic plague, a sneeze was believed to be a sign of impending death. 'God bless you' was 'a way of commending his soul to the care of God.' The phrase may have also come in handy to protect oneself if someone nearby sneezed."