Sinus squeeze is preventable in most cases by equalizing early and often during descent, keeping your sinuses clear before you dive, and using proper technique throughout the water column. The injury happens when a blocked sinus can’t match the rising water pressure around it, creating a vacuum that pulls on the sinus lining and causes swelling, fluid buildup, or bleeding. Understanding why it happens and what to do at each phase of a dive will keep you comfortable and injury-free.
Why Sinus Squeeze Happens
Your sinuses are air-filled cavities in the bones of your face, connected to your nasal passages through small openings called ostia. As you descend underwater, the water pressure increases, and the air inside those cavities compresses. This follows a basic gas law: as pressure rises, gas volume shrinks. If the ostia are open, air flows in from your nasal passages to balance the pressure automatically. If they’re blocked, the sinus becomes a sealed chamber with shrinking air volume, and the resulting negative pressure pulls on the mucosal lining. That’s the squeeze.
The frontal sinuses, located behind your forehead, are particularly vulnerable because their drainage passages are long and narrow, making them easy to block. But any of the four pairs of sinuses can be affected. The result ranges from mild pressure and discomfort to mucosal hemorrhage and sharp facial pain, depending on how much of a pressure difference builds up before something gives.
Equalize Before You Feel Pressure
The single most important rule for preventing sinus squeeze is to equalize before pain starts. Once a pressure differential locks the tissue in place, it becomes much harder to open those passages. Begin equalizing at the surface, before you even start your descent, and continue every meter or so on the way down. If you feel any tightness or pressure in your face, stop descending, ascend slightly, and try again. Never push through pain.
A slow, controlled descent rate gives you time to equalize properly. Rushing down, especially in the first 10 meters where the relative pressure changes are greatest, is one of the fastest ways to get squeezed. Descend feet-first if possible, since this positions your sinuses above your lungs and makes air movement through the passages easier.
Three Equalization Methods to Practice
Most divers learn equalization for their ears, but the same techniques help keep sinus passages open. Here are the three most common approaches:
- Valsalva maneuver: Pinch your nostrils against your mask skirt and gently blow through your nose. This creates overpressure in your throat that forces air up into your Eustachian tubes and sinus passages. It’s the most widely taught method, but it has a limitation: it doesn’t actively open the tubes, so it may not work if a pressure differential has already locked them shut. Blow gently. Forcing it can cause injury.
- Frenzel maneuver: Close your nostrils, close the back of your throat as if straining to lift something heavy, then make the sound of the letter “K.” This pushes the back of your tongue upward, compressing air against the openings of your Eustachian tubes. It’s considered safer than the Valsalva because it uses throat muscles to actively open the tubes rather than relying on raw air pressure.
- Toynbee maneuver: Pinch your nostrils and swallow. Swallowing pulls your Eustachian tubes open while the tongue movement, with your nose closed, compresses air against them. This is particularly useful during ascent if you feel a reverse block building.
Many experienced divers combine methods, swallowing while performing a gentle Frenzel, or alternating techniques as needed. Practice on land until the motions feel natural. If one method isn’t working underwater, try another before the pressure differential grows.
Keep Your Sinuses Clear Before You Dive
Anything that narrows or blocks the sinus ostia makes equalization harder. Congestion from a cold, allergies, or a sinus infection is the most common culprit. If your sinuses feel stuffed up on dive day, the safest choice is to skip the dive. No equalization technique can overcome a passage that’s swollen shut.
Some divers use decongestant sprays or tablets before diving to reduce swelling. This can work for mild congestion, but it carries a real risk: decongestants wear off. If the medication’s effect fades while you’re at depth, your sinus membranes can swell back up (a phenomenon called rebound congestion), trapping expanding air inside the sinus during ascent. The CDC lists overuse or prolonged use of decongestants as a specific risk factor for ear and sinus barotrauma in divers.
If you do use a decongestant, choose one with a duration of action that comfortably exceeds your planned dive time, and test it on a shallow dive first. Never rely on medication to push through congestion that you wouldn’t otherwise dive with.
Hydration and Mucus
Dehydration thickens nasal mucus, which slows the movement of secretions through the sinus passages and can contribute to blockages. Research in rhinology has confirmed that hydration directly alters the viscosity of nasal secretions: thicker mucus means slower drainage and a higher chance that an ostium gets plugged at the worst possible moment. Drink plenty of water in the hours before your dive, and limit alcohol and caffeine the night before, since both promote fluid loss.
Choose the Right Mask
Your mask creates its own air space over your eyes and nose, and that space is subject to the same pressure physics as your sinuses. As you descend, the air in your mask compresses, and the mask presses harder against your face. You equalize mask pressure by exhaling a small amount through your nose.
A low-volume mask requires less air to equalize and makes the whole process easier. High-volume masks need more air to balance, which can compete with the air your sinuses need. Masks that don’t cover the nose, like swim goggles, make equalization impossible and produce sustained pressure changes that can injure your eyes and sinuses. Always dive with a proper low-volume mask that allows you to pinch or press your nostrils closed.
Anatomical Factors That Increase Risk
Some people are structurally more prone to sinus squeeze. A deviated septum can restrict airflow to one side of the nasal cavity. Nasal polyps can physically block the ostia. Chronic sinus disease or scarring from previous sinus surgery can narrow drainage pathways permanently. If you repeatedly experience sinus squeeze despite good technique and clear sinuses, an evaluation by an ENT specialist may reveal an anatomical issue that can be corrected.
Reverse Squeeze During Ascent
Sinus squeeze doesn’t only happen on the way down. During ascent, the air inside your sinuses expands as water pressure drops. Normally this vents passively through the ostia with no effort required. But if mild swelling, mucus, or blood from a squeeze on descent has partially blocked those passages, expanding air gets trapped. The increasing pressure pushes outward on the sinus walls instead of escaping.
A reverse block typically announces itself as a sharp facial pain during ascent, often followed by a nosebleed or bloody postnasal drip. In severe cases, the pressure can rupture a thin sinus wall into an adjacent cavity. If you feel pain during ascent, slow down or stop and give the air time to work its way out. Gentle swallowing or jaw movements may help open the passages. Do not continue ascending rapidly through increasing pain.
Any bloody discharge from the nose or mouth after a dive needs medical evaluation. It can be difficult to determine whether bleeding originated from a sinus, the middle ear, or the lungs without proper examination.
What Sinus Barotrauma Feels Like
Mild sinus squeeze feels like sinus pressure or a dull ache behind the forehead, cheeks, or between the eyes during descent. If you equalize and the pressure resolves, no damage was done. More significant barotrauma produces sharp, localized facial pain that may persist after the dive, along with possible nosebleeds, blood-tinged mucus, or a feeling of fullness in the affected sinus. In severe cases, numbness in the face, persistent bleeding, or intense pain that doesn’t improve within a few hours indicates tissue damage that needs professional assessment.
Grading systems used in dive medicine range from Grade 0 (symptoms with no visible tissue damage) through progressively worse stages involving mucosal hemorrhage and, at the most severe end, structural damage. Most recreational divers who equalize properly and abort when something feels wrong never get past the mildest stage.