"I think it's a great approach," says Yehoash Raphael, an inner-ear biologist at the University of Michigan in Ann Arbor, who is also developing ways to regenerate hair cells. Raphael's group has had some success using gene therapy to convert other cells in the inner ear into hair cells. But he says ultimately it may be necessary to increase the number of cells in the inner ear, as Kil's group has done, rather than converting existing cells. Other scientists are studying other cell-cycle regulators with similar properties.

NIH's Battey also says the approach is promising, but cautions that for effective hearing-loss treatment, "just bringing hair cells back isn't enough, they must be wired correctly." They have to form proper connections, he says, so the central nervous system will interpret their input as meaningful sounds.

In fact, previous research suggests that getting these new hair cells to work properly might be tricky. Some animals genetically engineered to make extra hair cells have no or poor hearing, despite their ability to generate hair cells, says Raphael. "We don't yet know how to overcome that problem," he says. In addition, newly generated cells sometimes die.

"It's the right idea, but [gene expression] needs to be carefully controlled," says Douglas Cotanche, research director in the Department of Otolaryngology at Children's Hospital Boston. "You can't just knock down [the gene]...because the system recognizes that is not normal and cells die."

While still a long way off, such treatments might be ready by the time the iPod generation reaches its golden years. Experts predict that the high volumes and lengthy durations with typical iPod and MP3 player use will lead to serious hearing loss as today's young adults age. "I don't believe new treatment is right around the corner," says Battey, "but our children might benefit from hair-cell regeneration to replace lost cells."