 Welcome back to World Hearing Facts. I'm Susanna Love. It's a crazy fact that we really only have around 15,000 hearing hair cells in each ear, and that's not much. This is why we know that we need to protect them. But how much sound is too much sound? Here's a little background. We measure how soft or loud sounds are with a unit called decibels, or DB. The human ear is built to hear sound levels between around zero to 140 dB. Most of our time is spent at safe and comfortable listening levels, like these. Sometimes we're exposed to sounds that are painfully loud, and we can experience ringing or temporary hearing loss. That's our body's way of telling us that this is harmful. Our instinctive reaction is normally to cover our ears or to try to get away somehow. But what about those loud levels that many of us love, like listening to your favorite song and really immersing yourself in it? A movie theater experience, a video game with powerful sound effects. These examples can also be harmful. And this is where a guide or a rule of thumb might come in handy. So let's put down some ground rules. Above 85 dB, the hair cells in your ears really start to fight for survival. And if we don't give them breaks where they can rest and recover, then we risk damage over time. So your rule of thumb is the louder the sound, the shorter time you should be exposed to it. It's hard to estimate sound levels yourself, but luckily, there's many good smartphone apps out there that can help measure how loud your environment is. Let's take an example. If you're listening at 97 dB, your time should be limited to 30 minutes. If you turn the volume up to 100 dB, now you're down to 15 minutes. So for every 3 dB increase, you cut the time in half. Easy. That's it for now. Stay tuned for next episode where we take a tour through some of the loudest sound levels in the world.