Hearing loss is when your ability to hear is reduced. The most common causes are noise and ageing. When it occurs gradually overtime as a person ages, it is called presbycusis. About one-third of people in the United States between the ages of 65 and 75 have some degree of hearing loss. Hearing loss is defined as one of three types: conductive (involves outer or middle ear), sensorineural (involves inner ear), and mixed (combination of the two).