Beginner 6 minutes
The paranasal sinuses: the cavities you can't equalize on demand
Why a mild cold can ruin a dive and complicate your ascent
With your ears, you can do something about it: pinch your nose and blow. With the paranasal sinuses, there's no maneuver possible. They're either open or they're not, and that was decided by your health before you ever got in the water.
In this article you'll learn about the paranasal sinuses, why they behave like air spaces during a dive, how sinus barotrauma happens, and why ascending can be more problematic than descending.
It's the second most common pressure problem after the ears, and practically the only one that's completely prevented by a single decision: don't dive congested.
What they are and where they are
The paranasal sinuses are air-filled cavities hollowed out of the skull bones, around the nose and eyes. They come in four pairs: the frontal sinuses, above the eyebrows; the maxillary sinuses, under the cheekbones; the ethmoid sinuses, between the eyes; and the sphenoid sinuses, deeper, behind the nose.
Each sinus connects to the nasal passages through a narrow opening called an ostium. When those channels are open, air moves in and out freely and pressure equalizes on its own, without you having to do anything.
And that's the essential difference from the ear: there's no maneuver that opens a blocked ostium. With the middle ear, you can force air in through the eustachian tube; with a sinus blocked by mucus or inflammation, there's nothing you can do underwater.
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