Reverse Block in Freediving: What Happens on the Way Up

A reverse block happens when air trapped in your middle ear or sinuses can’t escape on the way up. As you ascend, the water pressure drops and that air expands, but a swollen Eustachian tube or blocked sinus opening stops it venting, so it presses outwards on the eardrum or the sinus lining. It usually shows up as pain, pressure or a sudden spin of vertigo in the last part of the ascent, and in most cases it is linked to congestion.

It gets less attention than the problems you have on the way down, which is exactly why it catches people out.

Why air needs to escape on the ascent

On the descent you actively push air into your middle ear to match the rising pressure. On the ascent the opposite happens, and normally you don’t have to do anything. The air expands, nudges the Eustachian tube open from the middle ear side, and slips out into the back of your nose. You might feel a squeak or a soft crackle. Air escapes outwards through the tube much more easily than it gets pushed in, which is why most ascents are painless.

The biggest expansion happens near the surface. Air in your middle ear at 10 metres doubles in volume by the time you reach the surface, as our post on pressure, depth and Boyle’s law shows. So if venting is going to fail, it tends to fail in those final metres.

What causes a reverse block

Anything that narrows the tubes or sinus openings after you have already equalised air into them:

• Diving with a cold or allergy. By far the most common cause. You manage to get air in on the way down, and the swollen lining won’t let it out.
• A decongestant wearing off. The tubes open on the first dives, then the medicine fades and the lining swells mid-session.
• Hard equalising earlier in the session. Forceful pushes irritate the tubes, and irritated tissue swells.
• Long sessions with many dives. Repeated pressure changes can leave the lining puffy by the end.
• Sinus problems such as polyps, a deviated septum or long-term sinusitis.

Our post on freediving with a cold explains why the first two are best avoided altogether.

What a reverse block feels like

	Squeeze on the way down	Reverse block on the way up
When	Descent	Ascent, often the last 10 m
Direction of force	Eardrum or sinus lining pulled inwards	Eardrum or sinus lining pushed outwards
In the ears	Pressure, then pain if you don’t equalise	Pressure or pain building as you rise, fullness afterwards
In the sinuses	Pain in forehead, cheeks or teeth	Same areas, often with blood in the mask on surfacing
Balance	Rarely affected	Brief vertigo if one ear vents and the other doesn’t

That vertigo has a name: alternobaric vertigo. When one ear releases pressure and the other doesn’t, your balance organs get conflicting signals and the world spins for a few seconds. Near the surface on a breath-hold, that is unpleasant and disorienting. A sinus reverse block, meanwhile, often ends with a nosebleed or bloody mucus in the mask. Our post on mask squeeze and sinus squeeze covers the sinus side in more detail.

What to do if it happens during the ascent

Your breath-hold comes first, as it does in every one of the freediving safety rules. You have limited air and the surface is where it is, so don’t stop and hang around trying to fix an ear.

1. Keep coming up. Slow the final metres a little if you have plenty in reserve, but never extend the dive for your ears.
2. Hold the line if you are diving on one, and keep your eyes on it if vertigo starts.
3. Try gentle swallowing or moving your jaw from side to side. Some divers find that pinching the nose and swallowing, the Toynbee manoeuvre, helps.
4. Don’t equalise. No Valsalva and no Frenzel. Both push more air in, which is the wrong direction.
5. Do your recovery breaths and surface protocol as normal once you are up. Our guide to recovery breathing covers those first seconds.

Scuba divers are often told to descend a little to relieve the pressure and try again. On a breath-hold, with limited air, that is rarely a good idea.

What your buddy should watch for

From the outside, a reverse block can look like a diver slowing unexpectedly, reaching for an ear, or grimacing in the last metres. With vertigo, they may surface disoriented, drift off the line or struggle to orient themselves. A good buddy meets them on the ascent, stays close and face to face at the surface, and watches them for longer than the usual 30 seconds. The diver may feel sick or unsteady even though their breath-hold went perfectly well.

Safety: Never prolong a breath-hold because of ear or sinus discomfort; surfacing with a sore ear beats a blackout every time. Tell your buddy as soon as you are up, end the session, and see a doctor or ENT if pain, vertigo, ringing, hearing loss or bleeding lasts.

After the dive: recovery and when to see an ENT

Mild reverse blocks often ease within minutes to hours as the lining settles and the trapped air finds its way out. Stay out of the water for the rest of the day, and don’t blow your nose hard.

See an ENT if:

• ear pain or fullness lasts more than a day
• your hearing is muffled, or you have ringing in the ear
• vertigo comes back or doesn’t settle
• there is blood or fluid coming from the ear
• you keep getting reverse blocks

Our guide to ear pain after freediving explains what each of these can mean.

How to prevent a reverse block

1. Don’t dive congested. If you can’t breathe easily through both nostrils, today isn’t the day.
2. Don’t rely on decongestants to get you through a session, and talk to your doctor about any medication you take.
3. Equalise gently and early on the way down, so the tubes don’t get irritated.
4. Treat a hard descent as a warning. If equalising took real effort on the way down, the way up may be difficult too. Shorten the session.
5. Leave decent rest between dives, and keep sessions shorter when you are coming back from illness.
6. Ascend smoothly. A relaxed, steady ascent gives your tubes time to vent through the final metres, where the expansion is greatest.

Your checklist before the next session

• Is your nose clear on both sides?
• Do both ears click with a gentle swallow?
• Will any medicine you have taken wear off halfway through the morning?
• Does your buddy know to watch you closely through the final metres?

If any answer worries you, swap the session for land work: equalisation drills, stretching and theory all count, and none of them need wet ears. We’re building an online community for Indian freedivers. It’s coming soon, so stay tuned.