Loud noise can cause injury by damaging the hair cells in the cochlea by bending and vibrating in response to sound. Loud sounds force those cells to flex with greater magnitude until eventually they break or wilt and don't respond to noise properly.
"If you beat on those hair cells hard enough they die," Rauch said. "Those cells never regenerate."
Since noise is a dose effect, sudden loud sounds can be just as if not more damaging than prolonged exposure to 80 Db of noise over eight hours in a factory, for example. A gunshot sounding at about 150 Db can do the same amount of damage in a fraction of a second as the accumulated injuries a musician might have, for example, and this can be an issue for war veterans, for example.
"Our ears really weren't meant to listen to music at the level we're listening to it for hours and hours," said Dr. Geroge Alexiades, an otologist and neuro-otologist at the New York Eye and Ear Infirmary.
But Alexiades pointed out that the problem is not necessarily having music playing so close to the ear but when that music is played loudly to drown out other sounds using earbuds that were not made to plug the ear canal.
"With earbuds that don't block background sound, people crank up their music louder," Alexiades said. "The intensity of sound we can listen to depends on how long we can listen to it."
Using ear buds can also demonstrate how hearing can change after long exposure to a certain noise level. Eventually, our ears undergo a temporary threshold shift, when our perception of normal volume changes and it is difficult to hear softer noises -- after a rock concert, for example.
The effect, however, is usually temporary and hearing will return to normal within several hours if no lasting damage was done.
While ear buds plug the ear canal and block ambient noise so that music may be played at a lower level, doctors caution that this can be dangerous in situations where noise cues are important for safety -- while driving or walking on a street, for example.
Diabetics are at risk for impaired hearing because their blood vessels are abnormal, Rauch said.
"Impairment of blood flow to the ear is bad," Rauch said. "It can go dead, like a stroke."
Narrow or abnormal blood vessels can prevent sufficient blood from reaching the cochlea as well as prevent toxins from getting cleaned out. This has the potential to damage the delicate cells within the ear.
"Diabetics can lose their hearing bit by bit," Rauch said. "It's not sudden deafness."
People with sickle cell anemia suffer from fatigue and pain because their red blood cells -- the vehicles for carrying oxygen and nutrients to cells and taking wastes away -- are misshapen. Such cells cannot transport as much energy to the body as normal blood cells do and their curved shape gives them the dangerous potential to slow down and clot.
Abnormally flowing blood can keep valuable nutrients from reaching cells in the ear.
"The ear has a high metabolic rate, it's active all the time -- you can't turn off ears," Rauch said. "With sickle cell anemia, you get sludging blood flow. A sickler might go deaf or lose their hearing suddenly because of a crisis."
The clanging, grinding, squeaking sound of a subway may be simply annoying to some, but regular riders are at risk for impaired hearing.