"Bless you"

why? why are these words spoken? There are varying accounts as to the origin of this response.  One belief is that it originated in Rome when the bubonic plague was raging through Europe. The pope gregory v11 beacuse otherwise it can contain death. 

When? When did this saying orginate? it orginate in AD 590 in rome when pope gregory V11 was there. 

How? How did this saying orginate? ordered unceasing prayer for divine intercession. Part of his command was that anyone sneezing be blessed immediately ("God bless you")

Where? Where did this saying orginate? it was in the 590 in Rome the PoPe gregory told other person cause it can contain death beacuse of the heart stoping.