While sleeping at night bacteria develop in the mouth, which generally results in bad breath. Most people find bad breath particularly offensive, and in numerous places throughout the Gemara, Chazal warn us about eating foods that cause it. Certainly if a person was preparing for an important meeting he would rinse out his mouth beforehand in order not to slight the honor of the person he is meeting.

Reciting numerous berachos to praise and thank Hashem is one of the first things we do every day upon awaking. Saying Hashem’s Name with bad breath indicates a lack of recognition of the purity and holiness of His Name (Beis Yosef 92). In this vein the Shulchan Aruch rules, “Some people have the custom to wash out their mouths in the morning” (Shulchan Aruch 4,17).

Although washing one’s mouth in the morning is certainly praiseworthy, it is not an obligation. Therefore, if there is no mouthwash or clean water available, he does not have to wait for them. Rather, he may go ahead and pray without rinsing his mouth (Mishnah Berurah 4,37).

Text Copyright © 2013 by Rabbi Daniel Travis and Torah.org