Contact hypersensitivity in patients with chronic otitis externa.

Thirty-seven patients with chronic otitis externa were investigated for contact hypersensitivity to 49 agents using standardized patch testing. Positive reactions were found in 22 (58%) patients. This incidence is higher than the 40% found in the only previous similar study and is within the range of 32-72% found in patients with contact dermatitis. The average age of subjects showing sensitivity was 56.7 years compared with 34.9 years for those with negative tests. This significant age difference suggests that contact hypersensitivity is not an aetiological factor in the younger patient. There was no significant difference in the duration of otitis externa between those with positive and negative tests. This feature has not been previously examined or reported. Neomycin was the commonest sensitizing agent, sensitization occurring in 12 (32%) patients.