why do they say bless you when you sneeze

They say "bless you" when someone sneezes for several historical and superstitious reasons. One popular origin is from the Middle Ages during the bubonic plague when sneezing was a symptom of the deadly disease; Pope Gregory I supposedly suggested saying "God bless you" to offer a prayer of protection and hope that the sneezer would not succumb to the illness. Another ancient belief was that sneezing could expel a person's soul from their body, so saying "bless you" was a way to protect the sneezer from evil spirits or the devil. Over time, the phrase became a polite social custom without the original superstitious meaning. Additionally, some cultures used similar phrases to wish health after a sneeze, such as the German word "Gesundheit" meaning "health".