Pure oxygen is a dry gas. The respiratory tract normally warms
humidifies and filters gases on inspiration but breathing dry
supplemental oxygen at increased flow rates may overwhelm
these systems. Subjective discomfort related to the drying of the
respiratory mucosa as well as adverse affects on the respiratory
mucous blanket and the activity of cilia may result. As a
consequence supplemental oxygen is routinely humidified,
although evidence to justify this is lacking