In short
- NHLBI lists dry mouth among the possible side effects of CPAP, along with congestion, runny nose and nosebleeds.
- In a 1996 study, a 10-minute mouth leak on nasal CPAP more than tripled nasal resistance in healthy volunteers, and a heated humidifier greatly reduced that effect.
- In a 2005 randomized trial of 98 new CPAP users, heated humidification didn't change how much people used CPAP but did reduce dry nose, mouth and throat.
- A 2018 meta-analysis of 13 trials found full-face (oronasal) masks were linked to higher pressures and about 48 fewer minutes of CPAP use a night than nasal masks.
- A 2025 randomized crossover trial of 62 people on CPAP who breathed through their mouths found average machine use rose by 51.8 minutes a day when mouth tape was added.
- In that 2025 trial, mouth and throat dryness improved with tape, adverse effects were reported, and the tape was used alongside CPAP, not in place of it.
Dry mouth with CPAP usually means air is leaking out through your mouth while you sleep. The National Heart, Lung, and Blood Institute (NHLBI) lists dry mouth among the common side effects of CPAP, and it's one of the most fixable. Heated humidification, a better mask fit, a chin strap or a different mask style each help many people, and your sleep team can adjust the setup with you.
Why does CPAP give you a dry mouth?
Research: moderate (what this means)CPAP gives you a dry mouth mostly when your mouth opens during sleep. With a nasal mask or nasal pillows, the machine's air is meant to flow in through your nose and stay in your airway. If your mouth falls open, that air can rush in through the nose and straight out through the mouth, drying everything it passes.
SleepApnea.org says you might not realize you're breathing through your mouth on CPAP, and lists these signs:
- waking with a dry mouth, sore throat or nasal congestion
- a partner noticing you snore even with CPAP on
- often waking tired or unrested
- breathing through your mouth as you fall asleep or during the day
Mouth leak also affects the nose. In a 1996 study in the American Journal of Respiratory and Critical Care Medicine, six healthy volunteers deliberately let air leak out of their mouths for 10 minutes while on nasal CPAP. Their nasal resistance rose from an average of 2.21 to a peak of 7.52 cm H2O/L/s, more than tripling. The researchers noted that nasal congestion, dry nose and throat, and sore throat affect about 40% of people on nasal CPAP. A stuffier nose then makes mouth breathing more likely, so the problem can feed itself.
What causes mouth leak on CPAP?
Mouth leak on CPAP usually comes down to a few things working together: the mask type, how dry the air is, a blocked nose, and sometimes the pressure settings or fit. The table below sums up the common causes and what people usually try.
| Cause | What you may notice | What usually helps |
|---|---|---|
| Mouth falls open with a nasal mask or pillows | Dry mouth on waking, snoring with CPAP on | Chin strap, full-face mask, talk to your sleep team |
| Dry air from the machine | Dry nose, mouth and throat | Heated humidifier, heated tubing |
| Blocked or stuffy nose | Congestion, breathing through the mouth | Humidification, treating the congestion with your doctor |
| Mask fit | Air hissing out at the edges, red marks | Refitting or trying a different size or style |
| Pressure settings | Leaks or mouth breathing that won't settle | A pressure review with your provider |
The mask itself matters. A nasal mask or nasal pillows leave your mouth uncovered, so any opening becomes a leak. A full-face mask covers both, which is why it's a common fix. A 2020 American Thoracic Society workshop report on mask selection looked at the breathing route during nasal and full-face CPAP, how air leaks happen, and options for controlling them, and recommended involving patients and their partners in choosing a mask.
Pressure and fit can play a part too. SleepApnea.org says persistent mouth breathing can reduce how well CPAP works, and may be a sign that your pressure settings, mask fit or equipment setup need adjusting. NHLBI says your provider can help you find a comfortable mask, use the humidifier and adjust pressure, or try a machine with auto-adjusting pressure.
Does a heated humidifier help dry mouth on CPAP?
A heated humidifier helps with dryness on CPAP, and this is one of the better-studied fixes. In a 2005 randomized trial in Chest, 98 people starting nasal CPAP were split into two groups, one with heated humidification from the start. Heated humidification didn't change how much people used CPAP or their quality of life, but dry nose and dry mouth and throat were significantly lower in the humidified group.
A 2011 randomized crossover study of 44 people in Sleep and Breathing tested a controlled heated breathing tube humidifier. Mouth dryness was lower with it from the first nights, and side effects kept improving over four weeks. As with the 2005 trial, quality of life and CPAP use didn't change, and people woke slightly more often from wetness on the face.
Heat seems to be the key. In the 1996 mouth leak study, a cold passover humidifier barely changed the rise in nasal resistance, while a heated water bath humidifier greatly reduced it, to a peak of 4.02 cm H2O/L/s.
SleepApnea.org suggests filling the humidifier reservoir to capacity before bed so it's nearly empty by morning, and mentions prescription nasal steroids as another option your doctor may suggest for congestion. If your machine has humidity and tube temperature settings, ask your provider which levels to try rather than guessing. Our guide to using a humidifier for sleep covers room humidity more broadly.
Do chin straps help with mouth breathing on CPAP?
Chin straps help some people keep their mouth closed on CPAP. SleepApnea.org says your doctor may recommend a chin strap so the air from the mask reaches your airway rather than escaping through your mouth. It also points out a limit: chin straps can hold the jaw closed but may not always stop air escaping through the lips.
If a chin strap leaves you with a dry mouth, that may be what's happening. Our article on chin straps for snoring explains how they work and who they suit.
Should you switch to a full-face mask?
A full-face mask is a common fix for dry mouth on CPAP, but it has trade-offs worth discussing first. SleepApnea.org says that if a chin strap doesn't stop air leaking through your mouth, your doctor may recommend a full-face mask, which sends air through both the nose and the mouth.
The research on full-face masks is mixed. A 2018 meta-analysis in Chest pooled 13 trials with 4,563 patients and found that, compared with nasal masks, full-face (oronasal) masks were linked to:
- a higher CPAP pressure, by about 1.5 cm H2O on average
- a higher leftover apnea-hypopnea index, by about 2.8 events an hour
- lower use, by about 48 minutes a night
Those are averages, and many people do well on full-face masks. But it's a reason to try sorting out the leak with a nasal mask first, and to make the switch with your sleep team rather than on your own.
What did the 2025 mouth tape and CPAP trial find?
The 2025 trial in the Journal of Clinical Sleep Medicine found that people who breathed through their mouths on CPAP used their machines more when mouth tape was added. It's a randomized trial, which makes it some of the stronger evidence on mouth tape, and its results are encouraging for this specific group.
The trial included 62 people with obstructive sleep apnea who breathed through their mouths on CPAP: 36 men and 26 women with an average age of 57.7. Each person used tape for 30 days and went without it for 30 days, in random order. With mouth tape:
- average CPAP use rose by 51.8 minutes a day
- the odds of good CPAP adherence were 4.5 times higher
- people reached at least 4 hours of CPAP use on 17.6% more days
- daytime sleepiness, snoring ratings and mouth and throat dryness also improved
Our article on mouth tape and CPAP goes through the trial in more detail.
What are the caveats?
The caveats matter here. The tape was used alongside CPAP, not in place of it, and the trial reported adverse effects with tape. It's one trial of 62 people, all of whom had sleep apnea and were already using CPAP.
The wider research on mouth taping is thin. A 2025 systematic review in PLOS One found that 4 of the 10 studies it included discussed a serious risk of asphyxiation if the mouth is sealed while the nose is blocked, and many studies excluded anyone with nasal obstruction.
Mouth tape is not a treatment for sleep apnea and doesn't replace CPAP. Our comparison of mouth tape vs CPAP explains why the two aren't interchangeable. If you'd like to try tape alongside CPAP, talk to your sleep doctor first, make sure you can breathe comfortably through your nose, and check that you can remove the tape easily. We don't recommend mouth tape for children.
Check this first. Skip mouth tape and see a doctor if you snore loudly, wake up gasping, have been told you stop breathing in your sleep, or can't breathe comfortably through your nose. More on safety
When should you talk to your sleep team?
Talk to your sleep team if dry mouth keeps coming back after you've tried humidifier changes, or if you notice leaks, snoring on CPAP or daytime tiredness. SleepApnea.org says persistent mouth breathing can reduce how well CPAP works. Your doctor can also look for causes that make nasal breathing harder, such as chronic congestion, allergies or a deviated septum.
NHLBI says getting used to CPAP takes time and patience, and that your provider can help you find a more comfortable mask, use the humidifier and adjust pressure settings. It also says to stop using your machine and call your provider right away if you get stomach discomfort or bloating.
Please don't stop CPAP because of dry mouth. It's a common side effect with several workable fixes, and your sleep team sees it often. Our overview of sleep apnea treatment options explains where CPAP fits. If your nose is the bottleneck, see how to unblock your nose before bed, and for dry mouth outside of CPAP, see why you wake up with a dry mouth.
This article is general information, not medical advice.
Read next
- Mouth tape and CPAP: what to know about mouth leaks, chin straps and full-face masks
- Mouth tape vs. CPAP: is mouth tape an alternative for sleep apnea?
- Sleep apnea treatments explained
Common questions
Why do I get a dry mouth with CPAP?
Usually because air is escaping through your mouth. When your mouth falls open with a nasal mask or nasal pillows, pressurized air flows in through the nose and out through the mouth, drying it. SleepApnea.org lists waking with a dry mouth, sore throat or congestion as signs you may be mouth breathing on CPAP.
Does a CPAP humidifier help dry mouth?
Heated humidification helps with dryness in trials. In a 2005 randomized trial of 98 new CPAP users, people given heated humidification had less dry nose and dry mouth and throat, though they didn't use CPAP more. A 2011 trial of a heated breathing tube also found less mouth dryness.
Should I switch to a full-face mask for dry mouth?
It's one option to discuss with your sleep team. A full-face mask covers the nose and mouth, so air isn't lost through the lips. But a 2018 meta-analysis found these masks were linked to higher pressures and lower nightly use than nasal masks, so many people try fixing the leak with a nasal mask first.
Can you use mouth tape with CPAP?
Only with your sleep doctor's agreement. A 2025 randomized crossover trial of 62 people with sleep apnea who breathed through their mouths on CPAP found they used their machines 51.8 more minutes a day with tape, and mouth and throat dryness improved. Adverse effects were reported, and tape was an add-on, not a CPAP replacement.
Do chin straps stop mouth breathing on CPAP?
They can help. SleepApnea.org says a doctor may recommend a chin strap to keep the mouth closed so CPAP air reaches the airway instead of escaping. It also notes that chin straps hold the jaw but may not always stop air escaping through the lips, which is why some people need a different mask.
When should I call my doctor about CPAP dry mouth?
Call if dry mouth keeps happening despite humidifier changes, or if you notice leaks, snoring on CPAP or daytime tiredness. SleepApnea.org says persistent mouth breathing can reduce how well CPAP works and may mean your pressure, mask fit or setup needs adjusting. NHLBI says to stop and call right away if you get stomach bloating.
Sources
- CPAP
- How to keep your mouth closed with CPAP
- Mouth leak with nasal continuous positive airway pressure increases nasal airway resistance
- Effect of heated humidification on compliance and quality of life in patients with sleep apnea using nasal continuous positive airway pressure
- Quality of life, compliance, sleep and nasopharyngeal side effects during CPAP therapy with and without controlled heated humidification
- Nasal vs oronasal CPAP for OSA treatment: a meta-analysis
- The importance of mask selection on continuous positive airway pressure outcomes for obstructive sleep apnea: an official American Thoracic Society workshop report
- The role of mouth tape for CPAP use in patients with mouth breathing and OSA
- Breaking social media fads and uncovering the safety and efficacy of mouth taping in patients with mouth breathing, sleep disordered breathing, or obstructive sleep apnea: a systematic review
About this article
- Research
- 9 published sources, listed above.
- Evidence
- Moderate. How we rate it
- Last checked
- October 14, 2026
- Funding
- Paid partner of Titan Recovery. Their ads are labeled.
- Found an error?
- Tell us. We log fixes on the corrections page.
* This content is for informational and educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any disease or health condition. Talk to a qualified healthcare provider about your health.