Your eardrum is a thin piece of skin stretched tight inside your ear, like the surface of a drum. When sound waves travel into your ear canal, they make this membrane vibrate, and those vibrations get passed along to tiny bones deeper in your ear that eventually turn them into signals your brain understands as sound.

The eardrum sits between the outer ear (the part you can see and touch) and the middle ear (where those tiny bones live). It's surprisingly delicate: a really loud explosion or even a bad ear infection can damage it. That's why doctors warn against sticking cotton swabs or other objects deep into your ears, since you could accidentally puncture your eardrum.

When you go up a mountain or take off in an airplane, you might feel pressure building in your ears. That happens because air pressure on one side of your eardrum differs from the other. Yawning or swallowing can help pop your ears by equalizing that pressure. Despite being thin enough to let you hear a whisper, your eardrum is tough enough to vibrate millions of times every day without wearing out.