What is the reason for this? The Ibn Ezra explains, “so that people won’t get harmed by his breath”. The Chizkuni also writes, “to block the bad breath that comes from his mouth, in order that other people won’t get harmed”.
The question is, a metzorah is supposed to be, בדד ישב חוץ למחנה - “sit in isolation outside the camp”, he isn’t even allowed to be with other people who have tzora’as. If so, why does he need to cover his mouth, who is going to catch anything? There is no one else around? Even during Corona, when people were away from other people there was no need for a mask?
The Darchei Chaim explains, that there were people that would bring food to the metzorah. To ensure that these people who were in contact with the metzorah for a few seconds didn’t get damaged, the metzorah was instructed to cover his mouth at all times. We see from here, how far one must go to ensure no damage comes as a result of him. The metzorah had to cover his mouth at all times, so that when for a few seconds people were near him, they would be protected.
R’ Chaim Ephraim Zeitchik suggests: “The haspoh [effect] of a metzorah effects the air, his horrible aveiros affect the air even when he is outside the camp, therefore, he has to cover his mouth. We see from here, how far one must distance himself from people who do aveiros and speak lashon hara.
