From Christina Aguilera's growling to Mariah Carey's range and emotional performances, singers can cause lasting damage to their voices.

Dr. John Schweinfurth, who specializes in otolaryngology at the Hershey Medical Center, said many sounds, whether growling and guttural or screaming can be very harmful.

"They are super hard of your larynx because of the amount of pressure and muscle tension," Schweinfurth said.

Schweinfurth said artists like Mariah Carey, in addition to her high pitch, make a lot of different sounds to add emotion.

Physical damage caused by creating those sounds can actually cause small bleeds or lesions to the vocal cords, which could lead to cysts down the road, Schweinfurth said.

"Singers, once they get a lesion, usually sing harder with more effort to get the sound they want, and eventually will crack one way or the other," Schweinfurth said.

"Vocal cords are relatively fragile; you can't do a lot of abuse to them," said Dr. Jan Hobbs, who specializes in otolaryngology at Medical Park Ear Nose and Throat in Lewisburg.

Hobbs said one simple example is hoarseness many people experience the day after cheering at a sporting event.

One sound that is sometimes made when singing, and even while just talking, is a vocal fry, explained Mary Saunders, who works in the music department at Penn State.

Saunders explained vocal frying stresses the vocal cords by interrupting the flow of air, which is the lubricant for the vocal cords.

Norman Spivey, a Penn State associate professor of music, said singer Christina Aguilera seems to start every phrase with a vocal fry.

Hobbs said it is possble to use false vocal cords, which lie just above the vocal words to speak or sing.

One example he gave is how Marlon Brando speaks in the movie The Godfather.

Using the false vocal cords can cause swelling that can affect the actual vocal cords, and over time can make it hard to maintain a youthful-sounding voice, Hobbs said.

Another way to cause damage Saunders said is screaming or even singing out of range.

"You can do one yell and do more damage than singing three songs," Saunders said.

Damage to vocal cords by either overuse or improper use can easily cause swelling.

With continued improper use, that swelling can lead to polyps on the vocal cords, Hobbs explained.

Those polyps can swell for a while, and with rest, could go away within a few months, Hobbs said.

However, if more damage is done, the polyps could develop into solid, hard nodules that are unlikely to ever go away, he added.

Damage to the vocal cords can be caused by repetitive use, much in the same way baseball players cause injury to their arms, and basketball players injure their knees, Hobbs said.

Damage done to the vocal cords can noticeably change a singer's voice, Hobbs said.

"Even someone like Cher has a much different voice than she used to years ago," Hobbs said.

Saunders said in addition to recording artists, opera singers and musical theater singers could also feel the effects of overusing their voices.

She said Broadway singers like Nathan Lane and Matthew Broderick, who are singing, dancing, and yelling at each performance, do at least six shows before they have a chance to rest their voice.

Schweinfurth said letting the voice rest is very important to maintaining it.

Artists like Celine Dion, who takes care of her voice by resting it during the day, will be able to sing well into their seventies, Schweinfurth said.

He said Dion knows what her limitations are.

"You have to be very aware of how you are using your voice," Spivey said.

Damage done to the vocal cords can eventually lead to scarring, which Schweinfurth said is "pretty much irreversible."

"Once you get scarring in the vocal cord, you're screwed," Schweinfurth said.