You wake with a mouth like paper. There are two causes and it is very common to have both at once: air escaping through your mouth, and air that was too dry to begin with.
Why it happens
With a nasal mask or nasal pillows, your mouth falls open once you are asleep. Pressurised air goes in through the nose and straight out through the mouth — a mouth leak — drying everything on the way past. You are effectively running a small wind tunnel through your face for six hours.
Low or absent humidification makes any leak far worse, and it does not take a desert to do it: winter air indoors is dry enough on its own.
The fixes, in order
- Turn the humidifier up. It is the single most effective change and the one most often left at whatever it shipped on.
- Add heated tubing if your machine takes it. It stops the condensation — rainout — that makes people turn the humidity back down and undo the fix they just made.
- If you breathe through your mouth, a chin strap or a switch to a full-face mask closes the escape route rather than trying to out-humidify it.
- Check the mask fit regardless. A leak anywhere dries you out, and dry mouth is often the first symptom of a seal problem you had not otherwise noticed.
It is not only a comfort problem
A mouth leak means pressure is escaping, which means the therapy you are getting is weaker than the therapy your machine believes it is delivering. The numbers drift, and the drift is confusing precisely because nothing feels obviously wrong except your mouth.
This is why fixing dry mouth so often fixes a leak nobody had diagnosed. Nightshift connects the two directly — 'dry this morning' logged against 'leaking at three' — so the pattern is visible rather than a suspicion.
Educational, not medical advice. Your sleep clinician sets your pressure and your settings.