Scuba Diving, Pressure, and Headaches

A diving headache almost always has one of four causes: carbon dioxide build-up from skip-breathing or over-exertion, sinus or middle-ear squeeze from failed equalisation, jaw and neck strain from gripping the regulator, or a mask strapped too tightly. Decompression illness is far down the list and usually comes with other symptoms. The pressure changes involved are enormous — descending ten metres doubles the absolute pressure on your body, a change roughly fifty times larger than a severe storm — but the body handles them well as long as the air spaces equalise.

Working out which of those four you have is straightforward once you know what to look for, and it changes what you should do about it.

The scale of the change

Water is dense. Every ten metres of seawater adds about one atmosphere, roughly 1,013 hectopascals, to the pressure on your body.

At the surface you are at one atmosphere. At 10 metres, two. At 20 metres, three. At 40 metres, the recreational limit, five. Going from the surface to 10 metres doubles the pressure. For comparison, the deepest Atlantic depression most people will ever sit through might move the barometer 40 hectopascals over a day.

Boyle's law explains why this matters most near the surface. The volume of a gas space halves between the surface and 10 metres, but only changes by a sixth between 30 and 40 metres. The first few metres of a descent are where ears and sinuses are most likely to be injured, which is exactly where divers tend to be least careful.

Your tissues are mostly water and are effectively incompressible. The trouble is confined to the gas spaces: middle ears, sinuses, the mask, the lungs, and the gut.

The four common causes

Carbon dioxide retention. This is the most frequent cause of a headache during or after a dive, and the most under-recognised. Divers often unconsciously skip-breathe to conserve air, or breathe shallowly against the resistance of a regulator. Carbon dioxide accumulates, and it is a powerful cerebral vasodilator. The result is a dull, diffuse, pressing headache that often peaks after surfacing rather than at depth. Exertion — finning against a current, a long swim back to the boat — makes it far more likely.

Sinus squeeze. If a sinus cannot equalise on descent, the pressure differential pulls fluid and eventually blood into the sinus cavity. This gives sharp, localised pain over the forehead or cheek that starts on descent and stops when you ascend a metre or two. Blood in the mask on surfacing is a classic sign and means the dive should end.

Middle ear squeeze. Failure to equalise the middle ear gives pain in the ear itself rather than the head, but it refers to the temple and jaw often enough to be described as a headache. This is barotrauma in the same family as ear pressure on flights, simply at a much steeper gradient.

Mask and equipment strain. A mask strap tightened hard leaves a band of pressure across the temples and the back of the head for hours. Clenching a regulator mouthpiece for an hour strains the temporomandibular joint and the muscles around it, producing a headache that is indistinguishable from a tension headache and often is one.

Less common but important

Mask squeeze occurs when a diver forgets to exhale through the nose on descent. The mask becomes a rigid low-pressure space against the face, drawing blood into the eyes and surrounding tissue. Alarming in appearance, usually not serious, but painful.

Cold-induced headache from cold water on the face or an ill-fitting hood is common in temperate diving and resolves on warming.

Decompression illness can present with headache, but it very rarely presents with headache alone. Look for it when there is joint pain, unusual fatigue, skin mottling, numbness, weakness, or confusion appearing within hours of surfacing. This is a medical emergency and needs a hyperbaric service, not painkillers.

Oxygen toxicity is a concern with enriched air mixes at depth, and headache can be a warning sign, though visual disturbance and twitching usually precede it.

Preventing it

• Descend slowly and equalise early, before you feel pressure. Start on the surface and equalise every metre for the first ten.
• Never dive with a cold or congested sinuses. This is the single most effective rule. Decongestants can wear off at depth and produce reverse block on ascent, which is worse.
• Breathe normally and continuously. Skip-breathing does not meaningfully save gas and reliably produces a headache.
• Loosen the mask. It should seal by suction, not by strap tension. If you are tightening it hard, the skirt is not sealing and a different mask would help.
• Stay warm and hydrated. Cold and dehydration both make headaches more likely and both worsen other diving risks.
• Pace the dive. Most carbon dioxide headaches follow a period of hard finning.

If you already get weather migraines

People who react to barometric change often assume diving will be intolerable. In practice it is frequently less of a problem than expected, and the reason is instructive: the pressure change in a dive is mostly conducted through incompressible tissue and is over quickly, whereas a weather system acts slowly on the whole body over many hours. Rate and magnitude are not the same thing as duration.

That said, migraine is common enough that some divers will have an attack that coincides with a dive, and telling a migraine apart from decompression illness underwater is genuinely difficult. This matters practically: if you have a history of migraine with aura, discuss it with a diving physician before certifying, because aura symptoms and neurological decompression illness overlap, and that overlap can complicate an emergency assessment.

Keeping a log helps. If you can show that your attacks track the current barometric pressure at home — somewhere with a genuinely active barometer such as Gulf Breeze, Florida, where Gulf frontal passages and tropical systems produce large seasonal swings — you have a baseline to compare a post-dive headache against. A migraine tracker app that records automatically gives you that history without needing to remember to log on a dive day.

FAQ

Can barometric pressure at the surface affect a dive?

Marginally. A low-pressure weather system reduces surface pressure by a percent or two, which slightly alters decompression calculations at the margin. The far more significant effect of bad weather is rough seas and the exertion and seasickness that come with them.

Should I fly after diving?

Not immediately. The standard guidance is to wait at least 12 hours after a single no-decompression dive and 18 hours after multiple dives or several days of diving, because cabin pressure at altitude reduces ambient pressure further. The mechanism behind that is covered in cabin pressure explained.

Why does my headache start after the dive rather than during it?

That pattern points strongly toward carbon dioxide retention. Levels build through the dive and the vasodilatory headache often peaks twenty to sixty minutes after surfacing.

Is a headache after every dive normal?

No. It is common, but it is not something to accept. A consistent post-dive headache almost always has a fixable cause — usually breathing pattern, mask fit, or exertion level.

When should I get checked?

Any headache accompanied by confusion, weakness, numbness, visual loss, difficulty speaking, or severe fatigue after a dive should be treated as possible decompression illness. Contact a diving emergency service immediately rather than waiting to see if it settles.