Nothing to Sneeze At
Question: If I am learning Torah and hear a nearby person sneeze, should I interrupt my study in order to wish him the traditional blessing of "labriyut"?
Answer: Whether it is the modern "labriyut" or the old-fashioned "gezuntheit", it is a hallowed tradition to wish one good health when we hear him sneeze. Whether one should do so even at the expense of a breach in his study of Torah was already discussed in the Talmud (Mesechta Brachot 53a). In the beit midrash of Rabban Gamliel they did not interrupt their study to wish "marpei" the original form of the blessing to one who sneezed.
Although this is the ruling of the Shulchan Aruch (Orach Chaim 246:17) there is a question raised by later authorities as to whether this also applies to our times when people interrupt their learning for other matters as well. There is a difference of opinion on this point between the Prisha and the Turei Zahav. The Aruch Hashulchan (ibid. 246:33) cites only the opinion of the Prisha that the restraint practiced in the beit midrash of Rabban Gamliel applies only to previous generations who never lifted their heads out of their sefarim, and that it is therefore quite in order for you to interrupt your learning to say "labriyut".