There are three types of hearing loss: conductive, sensorineural and mixed.
Conductive hearing loss occurs when sound does not travel efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear. This usually involves a reduction in sound level or the ability to hear faint sounds and can often be corrected medically or surgically.
Sensorineural is the most common type of permanent hearing loss and occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain. Most of the time, this cannot be medically or surgically corrected. Some possible causes are illnesses, drugs that are toxic to hearing, genetics or heredity, aging, head trauma, inner ear malformations or exposure to loud noises.
A combination of conductive and sensorineural. This is usually due to a combination of factors. Proper evaluation requires an examination of the ears as well as audiometric testing. Treatment will depend upon the causes.