How the sinuses lighten the skull
Sinuses are hollow, air-filled spaces within several bones around the nose and eyes. Because air weighs far less than bone, these spaces make parts of the skull lighter than they would be if the bones were solid. They also sit beside the nasal passages, where their lining helps warm and moisten incoming air.
Why a blocked opening can hurt
Each sinus drains through a small opening into the nasal passages. The openings are narrow, so swelling from a cold or allergies can restrict airflow and drainage. Mucus may then collect inside, and pressure can build as the lining becomes irritated. That combination can produce the familiar feeling of facial fullness or pain.
The sinus cavities are not sealed pressure chambers in the ordinary sense: they normally exchange air and drain through those openings. The discomfort comes when that exchange is impaired, not simply because the cavities exist.
A role in the sound of your voice
Sound from the larynx—the voice box—travels through the throat, mouth, and nose. The connected air spaces in the head help shape the sound by influencing how it resonates. When nasal passages are swollen, that route changes, which is why a stuffy nose can make speech sound different.
So the sinuses are part of a working system, not empty pockets whose only purpose is to cause congestion. Their small drainage pathways help keep them connected to the nose—and make them vulnerable when swelling narrows the way.
