Dry mouth at night can be considered as diabetes, hyperthyroidism, asthma, rhinitis, sinusitis, nasal polyps, and dry mouth at night can also be due to kidney deficiency and qi and blood deficiency. Diabetes causes dry mouth at night because of increased blood sugar, increased plasma osmolality, increased urination, and decreased water in the body. Hyperthyroidism can lead to nervous system dysfunction and thus increased sweating, resulting in more sweating and dry mouth at night. Asthma sleeps at night to breathe faster and deeper, resulting in faster evaporation of saliva in the mouth, so the mouth will feel dry at night. Rhinitis, sinusitis, and nasal polyps are due to poor breathing at night, and the mouth will open involuntarily at night to breathe, so the water in the respiratory tract evaporates more, so the mouth is dry at night. Urachalgia will also feel dry mouth, and there is the most serious immune disease called dry syndrome, which not only feels dry mouth at night, but also during the day.