Every CPAP mask leaks a little on purpose. Small vents let the air you breathe out escape, and your machine allows for that. The leak that matters is the unintentional kind: air escaping around the edges of the mask or out of your mouth.
Too much of it is a problem because your machine works by holding a steady pressure in your airway. When air pours out of a gap, that pressure drops, and the airway can collapse again. Leaks also dry out your eyes and mouth, make noise, and wake you up.
How much is too much?
ResMed machines treat unintentional leak above about 24 litres a minute as a large leak. Other brands measure leak differently (some report total leak, including the vents), so compare your numbers with your own usual nights rather than with someone else's machine.
In CPAPGeeks, look at Leak, 95th percentile on each night: it means 95% of the night your leak was at or below that number. On a ResMed machine, a night above 24 is worth a closer look, and the leak chart shows when it happened.
The usual causes, and what to try
The mask is too tight or too loose
Overtightening is the most common mistake: it creases the cushion and opens new gaps. Lie down in your sleeping position with the machine running, then loosen the straps until the leak stops and the mask still stays put.
The cushion is worn out
Cushions soften and lose their seal with use. A common replacement schedule is about once a month for a full-face cushion, and about every two weeks for nasal cushions or pillows. Check your supplier's or insurer's schedule.
Skin oil, lotion or a dirty cushion
Wash your face before bed, skip moisturiser where the cushion sits, and wipe the cushion every morning.
Your mouth opens
With a nasal mask or pillows, air can escape through your mouth. A chin strap helps some people. Treating a stuffy nose (for example with your humidifier) also helps, and some people do better with a full-face mask.
Sleeping position and pillows
Side and stomach sleeping can push the mask against the pillow and break the seal. A CPAP pillow with cut-outs gives the mask room.
Facial hair
Beards and moustaches leave small gaps. A trim, or a mask designed for facial hair, can fix it.
The wrong size or style
Faces change, and the mask you started with may not suit you any more. A different size or style (nasal pillows, nasal or full face) is often the real fix.
Leak still high? A professional mask fitting is often the fastest fix. Staff can watch the seal on your face at your pressure and try different sizes and styles with you. Your nearestCPAP Stores location can do a fitting.