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Background Cough originates from stimulation of structures innervated by the vagus nerve, including the airways and distal esophagus. Arnold nerve reflex describes the induction of cough by stimulation of the external auditory canal, which is innervated by the auricular branch of the vagus. Historically, the prevalence of this reflex has been reported in the range of 2% to 3% on the basis of studies of outpatients in otolaryngology practices, but has not been investigated in healthy volunteers or in patients with chronic cough. Methods Two hundred adults and 100 children with chronic cough, as well as 100 adult and 100 pediatric volunteers, underwent evaluation consisting of stimulation of the external auditory canal of each ear with a cotton-tipped applicator. Cough occurring within 10 seconds of stimulation was considered induced by the intervention. Results Arnold nerve reflex was present in 25.5% of adults and 3% of children with chronic cough. The prevalence of the reflex was 2% among healthy adults and children. In adults with chronic cough, Arnold nerve reflex was observed more commonly in women (31.6%) than men (12.5%) and was unilateral in the majority of patients (90.2%). Conclusions The greater than 12 fold prevalence of Arnold nerve reflex in adults with chronic cough compared with healthy volunteers supports the concept of cough hypersensitivity syndrome (CHS), in which vagal hypersensitivity is proposed to underlie chronic refractory cough. The absence of increased prevalence among children with chronic cough suggests that cough hypersensitivity syndrome is an acquired condition, perhaps triggered by viral respiratory infection or other environmental factor.