Four cavities that can't keep up

The sinuses are air locked inside bone. When outside pressure changes faster than they can equalise, you feel it.

You have four pairs of closed spaces in the facial skeleton, filled with air, connected to the outside world by narrow channels. That's the entire mechanism behind the pressure headache that's the best documented of them all. Not because the biology is complicated. Because it's mundane — so mundane that it has been given its own diagnostic code.

A headache with its own number

The International Classification of Headache Disorders, ICHD-3, has its own criterion: 10.1.2, "headache attributed to aeroplane travel". It's a recognition of something many travellers already know from their own body — but it's also a rarity. Most of the links this collection describes can't point to an official diagnosis with a number and a fixed cause. This one can.

What actually happens

The mechanism is an imbalance between the pressure inside the sinuses and the pressure outside. When a plane descends towards landing, cabin pressure rises faster than the narrow channels into the sinuses can equalise. The result is a kind of barotrauma — mechanical strain on the mucous membrane — probably reinforced by the body's own signalling substance prostaglandin E2 widening the blood vessels in the area.

The symptoms are distinctive enough to recognise: the headache typically sits on one side, around the eye or forehead, is severe and brief — and in over 90% of cases it occurs during the plane's descent, not during take-off or in the air. It usually clears again within 30 minutes of landing. Getting the diagnosis requires at least two episodes, and other headache disorders and genuine sinus problems must be ruled out first.

A whole field of its own

Air travel's pressurised cabins have given rise to a medical term all of their own: aerosinusitis, pressure-related damage and discomfort in the sinuses caused specifically by flying. That underlines the point: the physics behind airplane headache is so well-defined and reproducible that it has become a research field in its own right, separate from the more diffuse discussion of weather and headache in general.

That's also why airplane headache is useful to know about, even if you never set foot on a plane. It shows the mechanism in its purest form: no mixing it up with sleep, stress or diet, no doubt about what triggered it. Just four cavities that couldn't keep up.

The physics is the same, the strength isn't

The principle behind airplane headache isn't unique to a plane. Each of the four sinuses is a closed space trying to keep pace with a pressure moving outside it. What makes a plane the clearest example is the scale: an entire plane's cabin pressure changes markedly within a few minutes during descent, far faster than the narrow channels into the sinuses can keep up with. It's precisely that mismatch between the speed inside and outside that hurts — not the pressure itself.

Your home doesn't change pressure like a cabin

The pressure drop a plane cabin puts you through during a descent is far stronger and faster than what an ordinary low-pressure front does to the air around your home. Airplane headache is therefore the clearest, not the most common, example of the sinuses feeling the pressure. Most of your days don't bring a pressure change of that magnitude.