Why does otosclerosis often affect one ear before the other?

While it is a well-documented clinical observation that otosclerosis typically affects one ear before the other, the specific biological or physiological reason for this asymmetrical onset remains unknown.

The condition is characterized by the growth of abnormal, spongy bony tissue in the middle ear, which eventually welds the stapes (stirrup) against the surrounding bone, causing conductive hearing loss. Although the disorder is hereditary and often involves both ears eventually, the development of the initial nodule of softened bone is an unpredictable process.12

Research indicates that while these nodules are common—found in approximately 1 in 10 white adult men and 1 in 5 white adult women by middle age—they remain small and asymptomatic in the vast majority of cases. Because the exact cause of the nodule's expansion is not understood, medical science has not yet determined why the process initiates in one ear prior to the other.2