I've read the posts on this topic but remain unconvinced. The phenomenon occurs after some time with shallow dives (2-4m) and swimming (~1h) but without noticeable fatigue or exertion. It happens on the surface, so is not the 'mask squeeze' of scuba diving. It sometimes is accompanied with a kind of "knocking" sound as pulses of air are sucked into the nose. BUT - the air sucked in has nothing to do with lungs or breathing, which continues regularly, and it is unrelated to inhalation or exhalation and does not affect it in any way.
Lacking the expertise of an Ear, Nose and Throat physician, I can only surmise that the sucking somehow comes from the skull spaces, likely sinuses, I have no inkling of how it is possible.
The fact that it occurs after a long time has naught to do with fatigue - it might be due to sea water vapours from snorkel breathing possibly liquifying sinus mucus - how this creates a vacuum in the skull is beyond me.
It reminds me of sucking in air thru' the nose by sucking in back of oral cavity/upper throat that makes a snort, like when kids with a runny nose suck up the snot in it, except that that can't be done while breathing, but mask suck occurs while breathing.
After some time, when the mask is really tight, suction stops, probably because of pressure equalisation between mask and skull spaces. Releasing air into the mask, as others have observed, is only a short-lived solution, but is good enough, the whole thing is not a major problem, one exhales into the mask anyway to clear water now and again.
In sum, it's an interesting phenomenon, and I wonder if there are some good explanations out there.
Lacking the expertise of an Ear, Nose and Throat physician, I can only surmise that the sucking somehow comes from the skull spaces, likely sinuses, I have no inkling of how it is possible.
The fact that it occurs after a long time has naught to do with fatigue - it might be due to sea water vapours from snorkel breathing possibly liquifying sinus mucus - how this creates a vacuum in the skull is beyond me.
It reminds me of sucking in air thru' the nose by sucking in back of oral cavity/upper throat that makes a snort, like when kids with a runny nose suck up the snot in it, except that that can't be done while breathing, but mask suck occurs while breathing.
After some time, when the mask is really tight, suction stops, probably because of pressure equalisation between mask and skull spaces. Releasing air into the mask, as others have observed, is only a short-lived solution, but is good enough, the whole thing is not a major problem, one exhales into the mask anyway to clear water now and again.
In sum, it's an interesting phenomenon, and I wonder if there are some good explanations out there.