Barotrauma is an injury caused by an excessively fast change in external pressure (air or water) to the organs containing air cavities which contract (pressure increase) or dilate (pressure reduction) excessively.
Barotrauma may occur in unpressurised underwater diving (using bottles or free-diving) or in an unpressurised aircraft.
It can affect the inner ear, sinuses, lungs, gastrointestinal tract and teeth with caries.
Divers are at particular risk of barotrauma. The best countermeasure is good training. © Philippe Guillaume/ Flickr - Licence Creative Commons (by-nc-sa 2.0)