As a right one Muslim enjoys over another, one should reply to the person who sneezes.
Hadhrat Anas Bin Malik (رضى الله تعالى عنه) narrates that two people sneezed in the presence of Rasulullah (صلى الله عليه وسلم). He replied to one and not the other. The one who did not get the reply of Yar-Hamukullah said: “So and so sneezed and you replied but you did not do so when I sneezed?” The Holy Prophet (صلى الله عليه وسلم) replied: “He said “Alhumdulillah” whilst you failed to say Alhumdulillah.” [Muslim]
One of the etiquettes of sneezing is that the sound should be stilted and the nose covered. This ensures that one’s companion are not annoyed if anything comes out of his nose. In the event of any food or person before him, one should turn his face away and sneeze to prevent the particles that emerge from sneezing from falling onto the food or person before him.
Whenever our beloved Rasulullah صلى الله عليه وسلم sneezed, he would cover his face with his hands or with a piece of cloth, so that the sound of the sneeze could not be heard too loudly. [Tirmidhi]
Abu Musa al-Ash’ari (رضى الله تعالى عنه) said: I heard Allah’s messenger (صلى الله عليه وسلم) say, “When one of you sneezes and praises Allah, invoke a blessing on him, but if he does not praise Allah do not invoke a blessing on him.” [Muslim]
Source: The 40 Pathways to Jannah by Sheikh Khalid Sayyid Ali