"Bless You"
1. This words are said every time someone sneezes for many reason, some believe that sneezing is a way for the devil to enter the body, in which saying bless you keeps the demons outside, another reason is because saying bless you means that they hope you stay healthy and live many more years.

2.  This saying originated around AD 77, but it was said different, it was until AD 590 when Gregory 1 became pope and during the bubonic plague he established that saying bless you was how good health would be wished after sneezing, since sneezing was a sign of having the plague. 

3. Saying bless you might have started from ancient superstitions, also it was a way to wish good health to other people because sneezing would mean that you might have the bubonic plague, so bless you was a great way to wish good health.

4. The saying bless you has an unknown origin, and it isn't precise when it was first said either.