Relative humidity of the external auditory canal in normal and abnormal ears, and its pathogenic effect

To find the relative humidity of the normal external ear canal and to demonstrate that the relative humidity of the external auditory canal was higher in abnormal ears, i.e. ears commonly associated with chronic discharge.

Secondary health care within the ENT departments of Addenbrooke's and Hinchingbrooke hospitals.

A clinical observational study.

Volunteers seen in ENT outpatients. Inclusion criteria for the normal ear group, was a normal ear with no history of infection or previous ear disease. Inclusion criteria for abnormal ear group commonly associated with chronic discharge. Exclusion criteria were the presence of pus or infection within the ear canal.

The relative humidity of the external ear canal was measured in normal and abnormal ears. Abnormal ears were grouped as those commonly associated with chronic discharge, mastoid cavities, tympanic perforations, recurrent otitis externa and hearing-aided ears.

The range of relative humidity of normal ears is 40-70%. The humidity in abnormal ears was found to be significantly higher than the humidity in normal ears (P < 0.0001).

The raised relative humidity in the external canal may explain the predisposition of certain abnormal ears to chronic discharge and infection. If the humidity of the canal could be brought down to a normal level, this could offer a new therapeutic treatment.