Headphones are helpful. Many kids use them. But headphones can be harmful, too. They can cause hearing loss if the value（音量）is too loud. Studies show that one out of every ten kids in the United States has some hearing loss. The cause is loud noise.
Do you know how we hear? There are cells（细胞）inside the ears that help us hear. We can't see them with our eyes. "We call them hair cell," Jackie Clark said. "They look like hairs standing up." Clark is a scientist at the University of Texas. She studies noises and ears. Sound cannot be seen, but il can make the hair cells move back and forward. Think of the wind in the leaves.
Loud noises can damage（损伤）these cells. And once the cells are damaged，they don't grow back. Sometimes, there's tinnitus. "It's like someone is playing a note on the flute（长笛）for a long time." Clark says. It shows we're losing hearing. Tinnitus is not only harmful to our ears, also it can make us feel uneasy. That's why it's necessary to protect our ears.
How can we protect our ears? We'd better keep the volume low when we use our headphones. We should be able to hear sounds around us. And other people shouldn't hear noise from our headphones. "If I can hear what you're listening to when you're wearing your headphones," Clark says, "It's too loud." To protect our ears, keep our headphones at about half volume.
