Bad breath is mainly caused by low saliva secretion at night and food residues hidden in the crevices and gingival sulcus, which constantly breed bacteria. Therefore, it is recommended that patients who do need to stay up late should brush their teeth at 8 or 9 o’clock at night to clean the soft scales and food residues hidden in the gaps and gingival sulcus in a timely manner, or with a flosser or dental floss. Some patients like to drink coffee in the middle of the night, which contains certain sugar and is easily attached to the surface of the teeth or the tongue. If you really need to drink coffee, you can rinse your mouth with water after drinking coffee, which can reduce the bad breath caused by staying up late.