Definition
Inflammation of one or more of the sinus cavities caused by a pressure difference between the air trapped inside the sinus and the outside atmosphere, typically occurring during rapid changes in altitude when the sinus openings are blocked by congestion and cannot equalize pressure.
Plain English
Pain and swelling in the sinuses caused when air pressure inside the sinuses cannot equalize with the changing pressure outside during a climb or descent, usually because a cold or congestion is blocking the small passages that normally let air move in and out.
Context Anchor
Seen in aviation medical discussions, especially when deciding whether it is safe to fly with a cold, allergies, or sinus congestion.
Derivation
From Greek 'baros' meaning weight or pressure, plus 'sinus' (the air-filled cavity in the skull), plus the medical suffix '-itis' meaning inflammation. The 'baro-' prefix tells you the cause is pressure-related, which is why this only shows up in flying, diving, and similar pressure-changing activities.
Why Pilots Care
Untreated barosinusitis produces sharp pain that distracts from flying tasks and can force an early return or diversion.
Grounding Statement
Picture a small air pocket behind the cheek or forehead that cannot let air in or out as the airplane changes altitude; the pressure difference creates pain.
Intuition Check
Do not think of barosinusitis as just a regular sinus infection. The important aviation point is pressure change acting on trapped air in the sinuses.
Example Sentence 1
The instructor cancelled the lesson when the student mentioned a head cold, explaining that descending with blocked sinuses could trigger barosinusitis.
Example Sentence 2
A pilot with a head cold risks barosinusitis because blocked sinus passages cannot equalize with changing cabin pressure.