Praising Allah upon Sneezing and its Response
Abu Hurairah has related a Prophetic saying: "Allah likes sneezing and dislike yawning. When anyone of you sneezes he should say “Alhamdulillah” and the hearer thereof should respond “Yar hamakullah” as it is a right of the one who sneezes. (Sahih Bukhari).
There was a time when all observed these norms of Islamic behaviour, but now none even knows them, hence those norms have to revived.