What causes acute otitis externa?

External otitis is an extremely common condition and can affect between five to twenty per cent of the patients attending ENT clinics (Hawke et al., 1984). Its precise pathogenesis remains unclear, despite several aetiological classifications in the literature. The aim of this study was to investigate the relationship between infection, water exposure and trauma and the development of acute otitis externa. The study comprised 100 patients with their first attack of otitis externa and 150 age and sex matched controls. In only 40 per cent of cases could a primary microbiological cause be found. There was no significant statistical difference found between the two groups regarding the use of agents capable of traumatizing the external canal. Regular swimming, showering and hair washing were significantly more common in patients with acute otitis externa. Allergic disorders were nearly three times more common in the external otitis group suggesting a possible immunological aetiology.