You’re drifting off, or already asleep, when a sharp hissing or whistling sound cuts through, usually coming from somewhere around the mask seal. Sometimes it’s constant background noise you eventually tune out, other times it’s loud enough to wake you or your partner outright. It’s a different complaint from the general machine hum, this is a specific, sharper sound that tracks with air escaping somewhere it shouldn’t.

Why this happens

Hissing is the sound of pressurized air forcing its way through a small gap rather than flowing where it’s supposed to, usually around the edge of the mask cushion where it isn’t sealing fully against your skin. This happens for the same reasons general mask leak happens: a cushion that’s worn out and no longer holding its shape, a mask that shifted out of position during the night, straps that are too loose to hold a seal, or facial oils breaking down the grip between skin and silicone. Higher pressure settings make any small gap hiss louder, since more air is being forced through the same size opening.

Steps to troubleshoot

1. Check your leak data with your provider, since a hissing sound you notice is often reflected in elevated leak numbers on your device
2. Loosen the straps first rather than tightening them, since over-tightening distorts the cushion and can create new gaps instead of closing existing ones
3. Replace the cushion if it’s due, since worn silicone loses its ability to seal evenly even with a good fit technique
4. Refit the mask while lying down in your actual sleep position, since a seal that looks fine sitting up can hiss once you’re lying on your side
5. Clean the cushion daily to remove facial oils that reduce grip and let the seal slip under normal movement
6. If hissing keeps coming from the same spot despite these steps, ask about a different mask size or style, since a mismatch between mask shape and your face shape often shows up as a persistent, localized leak

Who to talk to

Your respiratory therapist can pinpoint exactly where the leak is coming from and refit you accordingly, or point you toward a different mask style if the current one keeps hissing in the same place. Your DME can process a cushion or mask exchange if a fit adjustment alone doesn’t resolve it. Your sleep doctor doesn’t typically need to be involved for hissing alone, but it’s worth mentioning if it’s paired with elevated leak numbers or if it’s disrupting your nightly use.

Evidence

Leak-related noise is one of the most common complaints reported by long-term CPAP users, with leak-related side effects reported by roughly three-quarters of patients in one large real-world study, and this type of side effect has been linked to both reduced adherence and residual daytime sleepiness.¹ Separate research measuring air leak directly found that patients who did not stick with therapy had meaningfully higher leak levels, adjusted for pressure, than those who did, reinforcing that addressing an audible leak isn’t just a comfort fix, it’s tied to how consistently people are able to use the therapy.²

References

1. Rotty MC, Suehs CM, Mallet JP, et al. Mask side-effects in long-term CPAP-patients impact adherence and sleepiness: the InterfaceVent real-life study. Respir Res. 2021;22(1):17.
2. Valentin A, Subramanian S, Quan SF, Berry RB, Parthasarathy S. Air leak is associated with poor adherence to autoPAP therapy. Sleep. 2011;34(6):801-806.