From ScienceDaily: "Age-related hearing loss is a very common symptom of aging in humans, and also is universal among mammal species, and it's one of the earliest detectable sensory changes in aging. ... In mice, the new study shows that the damage starts with free radicals, which are key suspects in many harmful changes of aging. Free radicals trigger a process called apoptosis, or programmed cell death, by which damaged cells 'commit suicide.' Apoptosis is often beneficial, as it eliminates cells that may be destined for cancer. Before the study, it was already clear [that] aging was associated with a major loss of hair cells and ganglion cells, so it was plausible that programmed cell death was playing a role in hearing loss. We also thought that oxidative stress - the presence of free radicals - contributes to age-related hearing loss, so we put two and two together and showed that oxidative stress does indeed induce age-related hearing loss. ... [Researchers] found that the suicide program was operating in hair cells and spiral ganglion neurons, and that the suicide program relied on activity in a suicide gene called bak. Activity of the bak gene [is] required for the development of age-related hearing loss. The strongest evidence for this was the fact that a strain of mice that did not have the bak gene did not show the expected hearing loss at 15 months of age."