Hair cell loss – cause or consequence of hearing loss?

Hair cell loss is a major hallmark of hearing loss. Historically, hair cell loss has been considered the major cause of hearing loss. Typically, synapses between hair cells and auditory nerve fibers and stereocilia are lost even before hair cells. Loss of these structures is often irreversible leading to permanent hearing loss. The earlier we can intervene in the course of hearing loss, the better we can maintain hearing function. Therefore, it is of importance to precisely understand the underlying causes and sequence of events leading to hearing loss. Notably, hearing loss precedes hair cell loss in many cases. Upon hearing loss, hair cells are present but exhibit morphological and functional defects. Thus, hair cell loss could merely be a secondary consequence of the loss of function of these sensory cells. Here, we review the literature highlighting that hair cell loss is often secondary to hearing loss. We suggest that hair cell loss is often rather the consequence than the cause of hearing loss.