Deafness may be congenital (present at birth) or acquired as a result of infection, trauma, or degeneration of the ear.

Deafness present at birth can be inherited (as is known to occur in certain American Paint horses) or result from toxic or viral damage to the developing unborn foal.

Acquired deafness may result from blockage of the external ear canal as occurs in longterm otitis externa (inflammation of the external ear canal), or it may occur after destruction or damage of the middle or inner ear. Other causes include trauma to the hard portion of the temporal bone that surrounds the inner ear, loud noises (for example, gunfire), conditions in which there is a loss or destruction of myelin (the fatty material that surrounds some nerve cells), drugs toxic to the ear (for example, aminoglycoside antibiotics or aspirin), and tumors involving the ear or brain stem. Deafness in one ear or partial hearing loss is possible in some of these instances (see Ear Disorders of Dogs: Deafness in Dogs).

Last full review/revision July 2011 by T. Mark Neer, DVM, DACVIM; Michele R. Rosenbaum, VMD, DACVD; Patricia D. White, DVM, MS, DACVD