Hearing loss is a spectrum with minor hearing problems at one end and profound, complete deafness at the other. Conductive hearing loss occurs when something blocks sound waves from reaching the inner ear. Sensorineural hearing loss is caused by damage to the inner ear or to the nerves that send sound to the brain. Sensorineural hearing loss is more likely to be permanent and to cause deafness. Sometimes a mixture of conductive and sensorineural hearing loss can occur.

Many different conditions lead to partial and total deafness. Ear infections and tumors can cause deafness because they cause conductive hearing loss - they obstruct sound from getting into the inner ear. Birth defects and diseases passed on by genes can do this too. Genetics is the major cause of sensorineural hearing loss. Half of all cases of profound deafness in children have a genetic source.

Presbycusia, or age-associated hearing loss, also has a genetic component. It's a condition that makes someone deaf over time as they age and is caused by the slow decay of sensitive hair cells lining the inner ear. As the hairs are lost, recognizing sounds becomes difficult or impossible. Hair cells can also be destroyed by high-pitched loud noise. A person is at a greater risk of going deaf if they had long-term exposure to the noise.

Some kinds of sensorineural deafness may be caused by infectious diseases, such as shingles, meningitis, and cytomegalovirus. In childhood, the auditory nerve can be damaged by mumps, meningitis, German measles (rubella), or inner ear infections. More rarely, the different viruses causing mumps, measles, flu, chickenpox, permanent or temporary, and often affects only one ear. If a woman contracts German measles during pregnancy, her child may have a permanent hearing disability. Lack of oxygen at birth can badly damage the ears and hearing.

Other causes of sensorineural hearing loss include diabetes, tumors of the brain or auditory nerve, and various brain and nerve disorders such as stroke. High doses of aspirin, quinine, some antibiotics, and diuretics used to treat high blood pressure may all permanently damage the inner ear. Nerve pathways in the brain that convey sound impulses can be damaged by multiple sclerosis and other diseases attacking the coverings of nerves. Violent injury and physical blows to the ear may cause permanent deafness.