Attending the latest concert? Cranking up your iPod? Using loud machines? All of these activities can result in irreversible damage to one’s ability to hear. And the number of those affected is on the rise. The number of Americans with some form of hearing disorder “has doubled since 1971,” Fox news recently reported , and Noise-Induced Hearing Loss (NIHL) is one of the most common forms.

While many understand that loud sounds can damage their hearing, few know why.

“[Heavy iPod use] can’t be good,” Daniel Long, a freshman in aerospace engineering, said. “I don’t know what it hurts or how much.”

“It hast to hurt your hearing, but I don’t know the degree of it,” Michael Biggerstaff, a freshman in industrial engineering, said.

Worse, some know full well that they are causing damage to their hearing.

“I know I am. I definitely am,” Dillon Love, a freshman in engineering, said. “I am definitely messing up my hearing with my iPod and stuff.”

NIHL is the result of damage to the ear’s hair cells. Located inside the cochlea, these cells are minutely small, yet vital to human hearing. When a sound wave comes through the outer and middle ear, it vibrates the cilia. The vibrations of the cilia complete a pathway for neurons to flow to the brain, resulting in the sensation of hearing. The more intense or loud a sound, the more violently the hair cells are shaken.

“When the sound is just to loud or to long for our system, these hairs can actually become sheared off,”Jane Lubischer, a professor of biology, said. “With too much movement you can get damage. Ringing in the ears is a pretty good sign you did some damage. You want to let it recover.”

An ordinary cut or even a broken bone can mend over time, especially in young people. What makes NIHL and hair cell damage frightening is that the damage is forever: hair cells cannot regenerate.

“If you lose one neuron in a pathway, that pathway is no good to you anymore,” Lubischer said. “It comes back to two things: how loud is the music and how long are you listening to that loud music,” Lubischer said. “There is some evidence that we can recover from short exposure to loud music, but you have to give your system time to recover. If you’re constantly bombarding it then you’re at risk for losing [hearing].”

A prime example of the danger of long-term exposure to loud noise is Pete Townshend, the guitarist and songwriter for the rock band “The Who.” According to Robert Grossfeld, a professor of biology, Townshend suffers severe hearing loss due to never wearing hearing protection while performing. Hearing loss is common among many musicians, not just rockers, says Grossfeld.

In addition to loud environments, Lubischer also warns of the risks to hearing regarding headphones.

“If you put the speakers right in your ear, one can imagine [the consequences], especially if you’ve got background noise,” Lubischer said. “If you’re in a quiet place you can have the volume down lower, but if you’re in a noisier background and crank up the noise to the point where you can hear it, then you can hear it but what your ear and hair cells are experiencing is a much larger volume.”

“Even though to us it’s just like ‘I’ll just turn it up loud enough so I can hear it,’ you’re at risk for putting it at a high volume that can cause damage,” Lubischer said. “That is the danger, and if you’ve got those ear-buds in all the time you’re not giving your hair cells a chance to recover. It’s definitely a hazard.”

There is hope, however, for regenerating hair cells.

“If we can understand at the basic science level, we might be able to move forward,” said Lubischer. “No promises, but that’s the hope.”

A. J. Hudspeth of Rockefeller University in New York is one of the leading researchers on the topic of hearing. Experiments on fruit flies have isolated the gene responsible for their hearing. Other research has found that amphibians are capable of regenerating hair cells. This knowledge may eventually lead to finding ways to regenerate human hair cells, but this may be farther out than many would like.

In the meantime, there are many ways to preserve one’s hearing. Specialized hearing protection is readily available for musicians, concertgoers, machinists, and mechanics alike.

As to iPod users, “Be sure you unplug for a while is my advice,” Lubischer said.