When air pressure is applied to the nose, the uvula and soft palate partially block off the mouth. Some air may escape from the mouth, called a “mouth leak,” which can be uncomfortable for a CPAP user. Most CPAP users learn to sleep with their mouth closed, even if they have been mouth breathers and snorers.
Unfortunately, larger mouth leaks will cause the CPAP pressure in your airway to drop. This drop in pressure may allow your airway to collapse and apneas to reoccur. However, various devices, such as chinstraps, may gently hold your mouth closed.