The most common type of hearing loss is presbycusis, or age-related hearing loss. Diminished hearing is a common side effect of aging, usually coming on gradually and affecting high-pitched sounds most frequently. It occurs as a result of natural changes in the inner ear of an individual over time. An estimated one third of adults aged 65 or older experience age-related hearing loss; that number jumps to nearly 50 percent by the age of 75. Presbycusis usually affects both ears equally. It may be mild, moderate or severe.