There are several reasons why one side of the nose is not ventilated when sleeping at night: 1, deviation of the nasal septum, deviation of the septum is generally an abnormality of the bone structure, when sleeping, especially when lying on the side, the nostrils facing upward are ventilated, the nostrils downward are not ventilated, and there will be alternating poor ventilation. You can do a nasal endoscopy to see if there is a deviation, and if the deviated septum affects sleep and work, it needs to be surgically removed; 2. Inflammation of the nasal cavity, such as unilateral sinusitis. Sometimes unilateral sinusitis may have nasal odor and a lot of pus nasal discharge, especially unilateral pus nasal discharge, which can also cause unilateral nasal ventilation at night when sleeping; 3, nasal polyps or papilloma, posterior nostril polyps are unilateral nasal growth, and papilloma is also unilateral nasal non-ventilation. Nasal endoscopy or sinus CT is needed to check; 4. Swellings in the nasopharynx, such as residual glands may block bilaterally or unilaterally. However, if there is a swelling in the posterior part of the nasal cavity a pathological examination is needed.