I know, I know ... You happened past an atheism blog and see its writer in cliche fashion talking about what to say (and not say) when people sneeze. And it's pretty typical for a new atheist to pronounce an edict that he'll never say, "Bless you," ever again! I'm also aware of how silly that is and for those who say, "If someone blesses me I'm gonna let them have it and tell them I don't believe in god so I don't need your worthless blessings for something so trivial!"
But, it's no secret that deconverting has its natural path, and that usually means investigating EVERYTHING that pops up that has some sort of religious connection. Before I became an atheist, I would always say bless you and frown when someone didn't. If they said gesundheit (German for health) or salute (Italian for good health) then that was cool, but if they said nothing? Well, then I was almost indignant. How dare they not care enough to bless my sneeze! Well, turns out, it truly is trivial, so much so that anyone who says bless you and doesn't understand why they say it makes for terrific fodder for those of us in the know. So, here's why:
The consensus is this sort of behavior started thousands of years ago, maybe even with the Romans, who were on record as saying, "Jupiter preserve you" or "Salve," which to this day still means "good health to you" in the formal Italian tongue. There have been other connotations of this behavior, including the Greeks, who would wish "long life."
"God bless you," according to Wikipedia, is attributed to Pope Gregory the Great, who uttered it in the sixth century during a bubonic plague epidemic (sneezing is an obvious symptom of one form of the plague). When someone says the German or Italian variations of "good health," it makes sense because a sneeze could mean you are coming down with a cold, so they are hoping you have good health and that the sneeze was an aberration.
According to Wiki: Virtually every country around the globe has its own way of wishing sneezers well. People in Arabic countries say, "Alhamdulillah," which means, "praise be to god." Hindus say, "Live!" or "Live well!" Some countries have special sneezing responses for children. In Russia, after children are given the traditional response, "bud zdorov" ("be healthy"), they are also told "rosti bolshoi" ("grow big"). When a child sneezes in China, he or she will hear "bai sui," which means, "may you live 100 years."
It goes on to say that ancient superstitions were also a part of the silly tradition. Some believed a sneeze causes the soul to escape through the nose, and that by saying "bless you" it would stop the devil from claiming the person's freed soul.
Others believed the opposite, that evil spirits use the sneeze as an opportunity to enter a person's body. When I was a kid, I was told (and I have no doubt my parents still believe this) the heart stopped or skipped a beat when you sneezed so if you said bless you it kind of asked god to spare you, or it was meant to welcome you back to life.
Think about how preposterous this is. Do you say anything when someone burps or farts (other than "You're disgusting!") in front of you? Of course it was science that proved a sneeze is a reflex to something tickling or affecting the inner workings of your nasal passage, such as a cold, dust, sunlight, etc.
So, if you're ever in my presence and you happen to sneeze, I won't be saying bless you. ... not because I'm an atheist, but because it's just plain stupid.