Before you spearfish — this comes first
- Get proper instruction before you spearfish. A recognised freediving or spearfishing course teaches the things that actually kill people in this sport, and reading about them is not the same as being taught them.
- Dive with a buddy, and dive one up, one down — one diver in the water, one on the surface watching them, every dive. A breath-hold blackout is silent and gives no warning; a watching buddy is the difference between an incident and a fatality.
- Stay inside your own training and experience. Depth and breath-hold times are personal, they change day to day, and nobody else's numbers apply to you.
- Understand the conditions before you enter the water: visibility, current, swell, tide, boat traffic and your exit. Conditions decide whether a dive is reasonable far more often than skill does.
- Use equipment you have been shown how to use, check it before every session, and be visible — a marked float and line are how boat traffic knows you are there.
- Never extend a dive for a fish. No catch is worth pushing a breath-hold, and the urge to take one more second is exactly what a blackout feels like from the inside — which is to say, like nothing at all.
Mask fogging, leaking and squeeze
Explainer · Last reviewed 2026-08-19
Three different problems with three different causes, routinely treated as one — and only the third has a safety consequence.
Safety
Shallow water blackout and breath-hold loss of consciousness — Can cause serious injury or death
The real danger of a fogging, leaking or squeezing mask is not the water. It is that a diver deals with it at depth — clearing, re-seating, adjusting — spending attention and gas at the phase of a breath-hold where neither can be spared, and sometimes reacting with a rushed ascent.
What reduces it: Fix mask problems on the surface, never at depth. A flooded mask can be ascended with, eyes shut, perfectly well — which is a thing worth having practised in a pool with an instructor rather than met for the first time on a reef.
Barotrauma and pressure injury — Can cause injury needing treatment
Unequalised mask squeeze pulls the mask onto the face as pressure rises and produces facial and eye bruising, and in severe cases injury to the eyes themselves.
What reduces it: Exhale a little air through the nose into the mask during descent, and turn the dive rather than push through a mask or ear that will not equalise.
Precautions that always apply here
- Never spearfish or freedive alone.
- Dive one up, one down: one diver down, one on the surface actively watching, every single dive.
FOGGING is condensation on a lens colder than the air inside the mask.
On a NEW mask it is caused by a release agent left on the glass from manufacture, and no defogger will work until that is removed — traditionally by scrubbing the inside of the lens with toothpaste or a dedicated cleaner until it squeaks. This step is skipped by most people and is why their new mask fogs no matter what they do.
After that, a wetting agent stops droplets forming: saliva, diluted baby shampoo, or commercial defog, applied and lightly rinsed.
LEAKING has two causes needing different responses. Hair under the skirt — including a moustache — breaks the seal and is fixed by clearing it or, for a moustache, a smear of grease along the skirt line. A mask that simply does not match the face shape cannot be fixed at all, which is why fit is tested by holding the mask on without the strap and inhaling gently through the nose: one that stays put has sealed.
A strap pulled tight to stop a leak makes it worse by deforming the skirt.
MASK SQUEEZE is the one that matters. On descent the air in the mask compresses and the pressure difference pulls the mask onto the face, rupturing small vessels around the eyes. It is prevented by exhaling a little air through the nose during descent, and it is a signal that equalisation technique needs attention rather than that the mask is faulty.
When a mask problem should end the dive
Most of the time a mask problem is an annoyance, and the honest answer is to surface, clear it and continue.
But two situations are different.
A MASK THAT CANNOT BE CLEARED IN COLD OR ROUGH WATER means a diver repeatedly stopping to deal with it, which costs warmth, time and attention — and attention is what the buddy system runs on. In marginal conditions that is a reason to end the session rather than persist.
A MASK SQUEEZE THAT HAS ALREADY OCCURRED means the diver was not equalising the mask on descent, and continuing to dive without addressing that is continuing to injure themselves. The dive ends, and the technique is corrected on land or with an instructor.
And there is a general principle here that recurs across this family: a small equipment problem in benign conditions is a nuisance, and the same problem in cold water, current or poor visibility is a reason to get out. The problem has not changed; the margin has.
All three are surface problems that get solved at depth, badly
Fogging, leaking and squeeze look like three separate nuisances and share one property that makes them worth a page: each of them is fixed on the surface in seconds and, if left, is dealt with at depth by a diver who should be doing nothing at all.
FOGGING IS A MANUFACTURING RESIDUE FIRST AND A TEMPERATURE PROBLEM SECOND. New silicone and glass carry a release film from moulding, and that film holds condensation no matter what is done to it afterwards — which is why a brand-new mask fogs relentlessly and a well-used one rarely does. Removing it properly, once, is the fix; anti-fog treatments applied over it are treating the symptom. After that, fogging is ordinary condensation and ordinary measures work.
LEAKING IS ALMOST ALWAYS SOMETHING UNDER THE SKIRT. Hair, the edge of a hood, a strap tab folded under, or the mask worn over a moustache. The second commonest cause is a strap done up too tight, which deforms the skirt and breaks the seal it was tightened to improve — a mask should be held on by suction and located by the strap, not clamped.
SQUEEZE IS PHYSICS AND IS THE ONE WITH CONSEQUENCES. The air in the mask compresses as pressure rises, pulling the mask onto the face, and it is relieved by exhaling a little air through the nose. On a breath-hold that air comes out of the only supply there is, which is the whole argument for a low-volume mask and is covered in `low-volume-masks-and-why-volume-matters`. Left unequalised, squeeze produces facial and eye bruising and, in the worst cases, damage to the eyes.
WHICH GIVES THE RULE THAT MATTERS MORE THAN ANY OF THE FIXES: DO NOT DIAGNOSE A MASK AT DEPTH. A diver clearing, re-seating, adjusting or refitting a mask at the bottom of a breath-hold is a diver whose attention and gas are going somewhere other than the dive, at the phase where neither can be spared. Surface, deal with it, go again.
AND A FLOODING MASK IS NOT AN EMERGENCY UNLESS IT IS TREATED AS ONE. A freediver can complete an ascent with a flooded mask, eyes shut, perfectly well. The danger is the reaction — the rushed ascent, the breath spent on clearing, the panic — rather than the water. That is a thing worth having practised in a pool with an instructor, which is one more entry on the list of what a course is for.
Authoritative guidance
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: Freediving safety practice: hypoxic blackout, its absence of warning symptoms, the ascent as the highest-risk phase, and the surface supervision that addresses it.States this directlyPassage read and verified
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Technical and sporting standards for underwater activities, including spearfishing conduct, technique convention and the safety expectations set by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated descriptions of established spearfishing practice and equipment convention, recorded as practitioner consensus rather than as scholarship.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where to go next
Where it matters
What these connections rest on (1)
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Spearfishing
A membership assertion rather than a topical one: this record teaches the discipline or its equipment, so the discipline's mandatory safety posture applies to it.
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Breath-hold spearfishing as a defined discipline with its own technical, equipment and safety standards, set out by the international underwater federation.States this directlyCitation checked — the work exists and is described correctly
- DAN guidance on freediving safety, hypoxia and shallow-water blackout — Divers Alert Network (Water-safety or diver-training authority)Relied on for: That the safety requirements of breath-hold diving apply across the discipline rather than to particular equipment or techniques within it.States this directlyPassage read and verified
Related reading
- Low-volume masks, and why volume mattersFogging, leaking and squeeze are the three ways a mask fails, they are all addressed before the dive rather than during it, and squeeze in particular is the direct consequence of the internal volume this record is about.
- Wetsuits, fins and masks for spearfishingThree different problems with three different causes, only one of which has a safety consequence.
What these connections rest on (2)
Practitioner consensus — 1 connection
Widely and independently recommended by experienced anglers and specialist sources. This is real angling knowledge, not proof: controlled evidence for it is limited, and FishingHQ records it as convention rather than as a demonstrated effect.
Low-volume masks, and why volume matters
A claim that this record rests on a mechanism explained elsewhere in the catalogue. It is the edge that makes the material an explanation rather than a list of equipment.
- BlueWater Hunting and Freediving — BlueWater Freedivers, Ventura, California, 1995 (Practitioner report)Relied on for: Established description of spearfishing equipment configuration, its failure modes and the reasoning behind rigging choices, recorded as practitioner literature.FishingHQ's interpretation of what it saysCitation checked — the work exists and is described correctly
- CMAS technical and sporting standards for underwater activities — Confédération Mondiale des Activités Subaquatiques (Standards body)Relied on for: Technical standards for underwater activities, including the equipment configuration and inspection practice expected of spearfishers.States this directlyCitation checked — the work exists and is described correctly
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: Widely restated descriptions of established spearfishing equipment practice and configuration, recorded as practitioner consensus rather than as scholarship.Background and mechanism onlyCitation checked — the work exists and is described correctly
Authoritative guidance — 1 connection
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Wetsuits, fins and masks for spearfishing
The equipment record and its commonest complaint.
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: Freediving equipment practice including mask fit, volume and equalisation.States this directlyCitation checked — the work exists and is described correctly
How this compares
- Equalisation and pressureMask squeeze is an equalisation failure rather than a faulty mask.
- Reading underwater conditionsA mask problem in benign water is a nuisance; the same problem in cold or rough water is a reason to get out.
What these connections rest on (2)
Authoritative guidance — 2 connections
Stated by a fisheries authority, scientific institute or recognised angling body. Authoritative, but summarising rather than demonstrating.
Equalisation and pressure
The one of the three that signals a technique problem.
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: Freediving equipment practice including mask fit, volume and equalisation.States this directlyCitation checked — the work exists and is described correctly
Reading underwater conditions
The margin changes even though the problem does not.
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: Freediving equipment practice including mask fit, volume and equalisation.States this directlyCitation checked — the work exists and is described correctly
Sources for this page
- AIDA International freediving education and safety standards — AIDA International (Water-safety or diver-training authority)Relied on for: Freediving equipment practice including mask fit, volume and equalisation.States this directlyCitation checked — the work exists and is described correctly
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