How does titanium's oxide surface film protect it from corrosion?

Titanium possesses excellent corrosion resistance in most natural environments due to the spontaneous formation of a passive oxide surface film.12

This film acts as a protective barrier because it is relatively inert chemically, effectively shielding the underlying metal from environmental degradation. This passive layer is so robust that the metal remains virtually unaffected even after prolonged exposure to seawater. Because of this property, titanium is highly valued for applications in marine environments, chemical processing, and medical prostheses, where it maintains its integrity despite contact with corrosive substances like salt solutions, body fluids, and various acids.213