CPAP Mask Fit: How to Find and Fix Air Leaks

Intentional venting versus unintentional leak

Every CPAP mask has small vent holes that let exhaled air (and the carbon dioxide in it) escape. That steady soft hiss is normal and necessary, so never block the vents.

Unintentional leak is air escaping where it should not, usually around the edge of the cushion or out of the mouth. Signs include hissing or whistling, air blowing into your eyes, a dry mouth, the mask making noise when you move, a partner complaining about noise, and leak warnings in your machine's app.

Reading your leak numbers

Machines report leak differently. ResMed devices show leak in litres per minute, and ResMed's own software treats a leak above about 24 L/min as high. Philips devices typically report the percentage of the night spent in large leak. Your app may simply show a mask seal score.

A single bad night is not cause for alarm. Look for patterns over a week, and bring your data to your DME or clinician if leaks are frequent. High leak can make the machine's estimate of your remaining breathing events (AHI) less reliable.

Step-by-step fit check

• Put the mask on while lying in your normal sleep position, with the machine running at its usual pressure. Many machines have a mask fit test feature that does exactly this.
• Start with the headgear loose, seat the cushion, then tighten evenly on both sides until the leak stops. Most leaks come from straps that are too tight, which buckles the cushion, rather than too loose.
• Check the cushion size. A cushion that is too large leaks at the corners; one that is too small presses on the nose or digs into the nostrils.
• Reposition before tightening. Pulling the mask away from your face slightly and letting it reinflate can reseat the cushion.

Worn or dirty parts cause leaks

Silicone cushions soften and lose their shape over time, and facial oils make them slippery. A cushion that sealed well when new can start leaking after a few weeks. Washing the cushion daily with mild soap and water, and washing your face before bed, helps the seal.

Headgear loses its stretch, so you end up overtightening. Follow your replacement schedule for cushions, pillows and headgear rather than waiting until they fail.

Position and pillows

Side sleeping can push the mask sideways against the pillow. Try a firmer pillow placed so the mask overhangs the edge, a CPAP pillow with cut-outs, or a smaller mask style. Hose tension also pulls masks out of position: route the tubing over the headboard or use a hose holder, and consider a mask with the hose attached at the top of the head.

If leaks begin later in the night, pressure may be rising (on auto machines) or you may be moving into a different position. Note when the leaks happen and share that with your provider.

When to ask for help

If you have tried a fit check, replaced worn parts and still leak, ask your DME for a refitting or a different style. Leaks that come mostly from the mouth call for a different approach, which we cover in our guide on mouth leaks. If leaks started after a change in pressure, weight or dental work, mention that to your clinician.