Remember the classic Seinfeld episode regarding the sneeze? Well that's an unfair question for two reasons. First, there were WAY too many Seinfeld episodes that can be deemed as classics to actually know which one I'm referring to. Secondly, there were actually two that contained a reference to sneezing where that was a focal point of the episode. If you're a true Seinfeld aficionado, you will know right off the bat from the title, which one I'm referring to.
Long story short, the Seinfeld gang had surmised that when you sneeze, why say "God bless you"? They didn't go into the religious overtones of it, but they agreed that it's better off to say "You're so good lookin'".
I've long been an opponent of the saying "God bless you" thing when people sneeze too. A lot of people just say it as an unconscious reflex and don't have any idea where it came from. There are two schools of thought as to why it's done. The first is the historical reference behind it. In earlier times, it was believed that when you sneezed, you opened yourself and your soul to the outside world. It was an unnatural and certainly a bizarre happening and clearly portended evil. It was thought that your soul might escape, or demons and evil spirits might get in, or even that they may have caused the sneeze in the first place. The blessing was to help ward off such badness.
The second philosophy was a scientific one in that people had perpetuated the myth that when you sneeze, your heart stops so that's why the blessing was given. This has been discounted by doctors. It has been proven that a sneeze itself is a very brief event, occurring in a shorter time than a heartbeat. I did even more reserach and found doctors indicate that heart beats because a small part of it called the SA node that has a "pacemaker" activity. What this means is that there is a type of electrical cycle going on that triggers beats roughly once every second. Sneezing does not change the electrical cycle so the heart keeps beating.
In essence, the common "God bless you" phrase after a sneeze wouldn't seem appropriate when you consider the context in which it's being used. But if you don't say anything, are you just being flat out rude? That then brings up the other Seinfeld episode that comes to mind where George blesses the wife's sneeze because the husband didn't.
At any rate, it seems as though it would still be okay to say "God bless you" because after all, we could all use His blessings anyway. The sneeze is just a convenient way for us to slip it in there as a reminder.