If it’s a friend, I tell them to settle down. Otherwise “Gesundheit” or “Bless you.” I don’t care about the God thing; it’s just a figure of speech.
Nice catch!
I say nothing.
But some friends at work came up with something in case we are perceived as being rude by not blessing. We say, “I acknowledge the fact that you sneezed.”
This seems relevant…
My thoughts exactly! Why do we feel the need to say anything after someone sneezes? It is an old tradition that is no longer needed.
Hail sneezer.
I don’t say anything, and I’m a bit weird in that I don’t like it when anyone says anything to me when I sneeze. I guess I get a bit embarrassed when I sneeze, and I don’t like people calling attention to it.
That’s pretty much me. I’m an atheist, but still culturally Christian to a certain degree. It’s what I grew up with, like celebrating Christmas.
I asked my mother what the traditional Japanese response is, and she said nobody says anything. A few years ago, a Chinese language teacher told me the Chinese have no traditional response, either.
Way back in elementary school, I learned that “God Bless you!” was a Dark Ages response because people believed The Devil entered you through your nose and that tickly sensation was what made you sneeze. Obviously, that was a Christian concept. That teacher noted that “Gesundheit” was merely German for the same well wishes, literally breaking down to “God Send Health [to you].”
Later, a Jr. High history teacher explained that people in the Renaissance era said “Bless You” because a sneeze was a potential indicator of poor health – susceptibility to the Black Death that was going around at the time. (This is the teacher who taught us the real meaning of the Ring around the rosy rhyme, as well).
Over the years, as I became more rooted in my anti-monotheism/atheism/non-theism I started substituting other responses*. Salud (Health [to you]) is familiar enough here in southern California, Bon soi is the closest I could figure out for French, and my Russian teacher told me kchort is an insult when taken literally but is received as the reverse – kind of like telling an actor to ‘break a leg’ before a performance.
So my first three responses are typically, “Salud!..Bon soi!..Kchort!” and that tends to be all that’s needed.
And recently my father-in-law told me he grew up with Prosit in his household. His family is Danish but he noted that it’s a Swedish term that everyone used for some reason. I’ll add prosit to my recitals, if necessary. But usually when my father-in-law is visiting, we respond to each other’s sneezes by rating them like gymnastics or figure skating performances. He and I are particularly loud sneezers, so we make a joke out of it by turning it into a competition. 
–G!
*My friends learned to respond to my sneezed with “Blast you!..Damn you!..Shut up already!”
I don’t say anything - never saw the point (and while an atheist, don’t really think of that as a particularly “atheist” point of view - I have zero problem with saying “Merry Christmas” or whatever.)
Other.
I say nothing.
I don’t say anything, unless it’s unusually loud, in which case I say “Woah there!” or something equally exclamatory.
Spaniard here. I will say “Jesús”, which is the standard response to sneezing in Spain, whether you are a good catholic, a good atheist, or a faithful follower of the Flying Spaghetti Monster.
I don’t react at all.
Nothing.