Why Your CPAP Mask Isn't Sealing — And How to Fix It

A mask that won't seal is the most common reason CPAP users give up on therapy. The air whistles, the cushion creeps, the strap gets tightened until it leaves a mark on your forehead — and the next morning the machine reports a leak rate that's far above target. The frustrating thing is that mask leak is almost always fixable, and it almost never requires buying a new mask outright. Six causes account for nearly all leak problems we see. Here they are, ranked by how often they're the actual culprit.

1. The cushion is past its replacement date

Mask cushions are made of medical-grade silicone, and silicone slowly loses its elasticity from the moment it's manufactured. Combine that with nightly exposure to skin oils, sweat, and warm air, and a cushion's seal performance degrades noticeably by month three. By month six, most cushions can't hold a clean seal regardless of strap tension.

The kicker: cushions don't look obviously worn at three months. The silicone still looks pink-and-clean. What's changed is the flex — the cushion no longer rebounds to fill small gaps as you shift in your sleep. If your last cushion swap was more than 90 days ago, that's almost certainly your leak source. Replace it. Our cushion replacements ship next-day, and our 30-day fit guarantee covers a free swap if you got the wrong size.

2. The mask is the wrong size

Most masks come in S/M/L (some in XS and XL too). The size affects seal more than most users realize — a Medium cushion on someone who needs a Small will never fully seal, no matter how tight the headgear. Manufacturer fit guides exist for a reason: ResMed's mask-fit templates are printable PDFs that show life-size outlines you can hold up to your face.

Signs you have the wrong size

• Too small: the cushion creates pressure points on the bridge of your nose, leaves deep marks in the morning, and leaks at the upper edges as pressure ramps up.
• Too large: the cushion sits low on your nose, leaks downward (toward your mouth), and you find yourself tightening straps to a degree that's uncomfortable.

3. The headgear is over-tightened

This is counterintuitive but real: tightening the headgear to chase a seal usually makes the leak worse. The cushion is designed to seal with mild positive pressure from the CPAP — when straps over-compress the silicone, it deforms and creates new leak paths.

Correct technique: loosen the straps as much as possible before putting the mask on. Lie down in your normal sleep position. Turn the machine on. Then tighten straps in quarter-inch increments only until the leak stops. Most masks are designed to seal with surprisingly low strap tension.

4. Sleep position changed

Mask fit changes between sitting up, lying on your back, and lying on your side. A mask that seals beautifully when you fit it at the edge of the bed may leak the moment you lie down. The most common manifestation: the cushion presses into the bed when you side-sleep, deforming the seal on that side.

Two fixes. First, fit the mask in your actual sleep position — lie down before tightening straps. Second, if you're a dedicated side-sleeper, consider a mask designed for it — see our guide to the best CPAP masks for side sleepers.

5. Mouth breathing

If you wear a nasal pillow or nasal mask and your mouth opens during sleep, the pressurized air bypasses the seal entirely — exiting through your mouth. This isn't technically a mask leak (the cushion is fine), but it shows up on your machine's leak report the same way and produces the same dry-mouth-in-the-morning symptom.

Three options, in order of how much effort each requires:

1. Chinstrap. A soft strap that holds your jaw closed. Works for some people, drives others crazy.
2. Mouth tape. Hypoallergenic medical tape applied gently across the lips. Sounds extreme, works surprisingly well for many users.
3. Switch to a full-face mask. The right answer if mouth breathing is chronic. See our full-face cushions if you already have a compatible frame.

See our deeper article on mouth breathing on CPAP for the diagnostic flow.

6. The mask is the wrong style for your face

This is the last thing to consider, but for some users it's the actual answer. Mask style — nasal pillow, nasal cradle, full face — interacts with facial geometry, breathing pattern, and pressure setting in non-obvious ways. The signs your style is wrong (rather than your size or your wear):

• Nasal pillow leaking at higher pressures (10+ cmH₂O). Nasal pillows struggle to seal at high pressures because the seal area is so small. Most users at 12+ cmH₂O do better with a nasal cradle (N20-style) or full-face mask.
• Mustache or beard interference. Facial hair compromises the seal area for nasal-cradle and full-face masks. Nasal pillows fit independently of facial hair and are often the right answer for bearded users.
• Glasses incompatibility. The DreamWear style (which seals around the nose, with the air tube routing over the head) leaves the bridge of the nose completely free — useful for people who read before bed.

What to check, in order

If your mask is leaking tonight, run through this checklist:

1. Cushion older than 3 months? Replace it.
2. Cushion the right size? Use a manufacturer fit guide.
3. Loosen the headgear, put the mask on, lie down, then tighten.
4. Is your mouth opening? Try tape or a chinstrap for one night.
5. Are you on a side-sleeper-friendly mask if you side-sleep?
6. Have you outgrown your style? Pressure changes are a common trigger.

The cost of ignoring leak

A leak rate above target (usually >24 L/min on ResMed reports) doesn't just mean wasted air. It means the machine is delivering less effective pressure to your airway, which lets apneas slip through — which is why your machine's AHI score rises in lockstep with cushion wear. The CPAP can compensate up to a point by ramping pressure, but a chronically leaking mask defeats the therapy.

Most leak problems are fixed with a $20 cushion swap. The hardest part is doing it before the leak gets bad enough to remember.