External auditory canal pH in chronic otitis externa.

Several risk factors have been postulated to play a part in the progression of acute into chronic otitis externa, including changes towards alkalinity of the skin pH of the external auditory canal. These changes have been previously reported to occur in the acute stage, and their persistence may predispose to a chronic status of this condition. This prospective control study was designed to look at this possible relationship in more depth, by comparing the external auditory canal pH of individuals with chronic otitis externa, but with no current exacerbation, with an age-/sex-matched control group. Analysis of the data revealed a significantly higher external auditory canal pH in the chronic otitis externa group (P < 0.004) when compared with the controls, with no concomitant difference in body skin pH. Within this chronic otitis externa cohort, a statistically significant correlation was found between external auditory canal pH and the severity of the condition, as assessed using a multiparameter scoring system (r = 0.562; P < 0.02). Importantly, the pH was not related to the length of time since the last exacerbation. There was a significant age relationship present within our sample. Younger patients displayed more severe chronic otitis externa(r = -0.813; P < 0.001), with correspondingly higher external auditory canal pH values (r = -0.550; P < 0.02). The results suggest that alkaline ear canal skin is a local risk factor for the progression into chronic otitis externa, occurring, in this study, with greater severity in younger individuals.