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  • [♪ INTRO]

  • Take a moment and listen carefully to all the noises around you.

  • If you hear your neighbor's music, the hum of a nearby highway, or the clatter of a passing train,

  • that's a sound that could be killing you.

  • Ok, not right away, and not all by itself,

  • but the sounds we hear every day really do have effects on our health.

  • Not just our ears, but our hearts and even our brains.

  • So what we hear as sound is actually pressure waves traveling through the air around us.

  • And like any wave, sound carries energy.

  • We usually talk about that energy in a unit called the decibel,

  • but what decibels actually are is a little complicated.

  • Every decibel is actually one-tenth of a bel, named for the inventor of the telephone, Alexander Graham Bell.

  • And for weird historical reasons, the bel exists mainly in your physics textbook.

  • And decibels rule the rest of the world.

  • The decibel scale isn't linear, it's logarithmic.

  • As the number of decibels increases, the amount of sound energy goes up exponentially,

  • rather than at a constant rate.

  • That means twice as many decibels isn't twice as noisy,

  • it's the difference between a loud conversation and the deck of an aircraft carrier.

  • Because of the way our brains process sound,

  • 10 times more sound energy means we hear something as being only twice as loud.

  • So yeah, decibels are weird, but so are our brains.

  • Our ears also aren't equally sensitive to all frequencies,

  • so you might hear two sounds with the same power at totally different volumes.

  • So to correct for that and make loudness values more intuitive,

  • scientists use the A-weighted decibel scale.

  • Today, we're going to focus entirely on sounds that we can actually hear,

  • but we're also constantly hit with frequencies above and below that range.

  • Scientists know less about how these other kinds of sound affect us,

  • but it's still out there and still has energy, so we probably interact with it on some level.

  • For example there's some evidence that infrasound, below the range of our hearing,

  • might be part of what leads people to think they've seen stuff like ghosts.

  • Now, we all know that loud abrupt noises like firecrackers can damage our hearing.

  • But exposure to lower-level noise is still dangerous.

  • Even if it's not enough to make you goow, my ears.”

  • And it's not your eardrum that gets hurt.

  • It's your hairs.

  • That is, the tiny hair-like sensors called hair cells inside your ear.

  • The process that turns pressure waves in the air into the sounds in your brain is not simple.

  • It starts with your eardrum, which vibrates as each wave hits it.

  • Those vibrations shake three tiny bones inside your ear, which in turn shake the cochlea,

  • a pocket of fluid shaped kind of like a snail's shell.

  • And now comes the key part, embedded inside the cochlea are around 16,000 tiny hair cells.

  • As they move with the fluid, some hair cells generate electrical signals

  • that are carried by the auditory nerve to your brain.

  • That's how you hear.

  • The louder the noise, the more those hair cells move and the stronger the signals they produce.

  • But if there's too much movement, as in a sound that is too loud,

  • and the hair cell can become damaged.

  • We can lose 30-50% of them before noticing our hearing start to decline.

  • Hair cells can bounce back to some degree, but too much damage will destroy them.

  • They don't regrow, and no treatment currently in use can bring them back.

  • Sometimes that hearing loss manifests itself as just being harder to hear.

  • Other times, you can get tinnitus, which sounds like a ringing in the ears that just won't go away.

  • 15-20% of people will get at least mild tinnitus in their lives, often as a result of old age.

  • But persistent loud noises can bring on tinnitus more strongly and earlier in your life.

  • Like for example, if you were to tour in a rock band ever.

  • Fortunately, the CDC and the World Health Organization have figured out what sound levels are safe,

  • and it's not too bad.

  • Basically, anything below about 85 decibels is safe for an eight-hour work day.

  • As we've explained, decibels aren't terribly intuitive.

  • But a good rule of thumb is that if you've got to raise your voice to talk to someone an arm's length away,

  • your environment is louder than eighty-five decibels.

  • A hockey game at 95 decibels is safe for only 47 minutes, a 100 decibel nightclub just 15,

  • and a 120 decibel drum set is okay for just 9 seconds a day.

  • So being a drummer definitionally is an unsafe work environment, so bless them all.

  • Of course, these values are averaged across lots of people in many different circumstances,

  • but every time you cross the threshold, you're taking a chance with your ear hairs.

  • One risky behavior many of us do every day is listening to music through our headphones.

  • At max volume, an iPhone puts out around 100 decibels,

  • which, again, is safe for only a few minutes a day.

  • To listen safely eight hours a day, you want to keep that slider around 70% or less.

  • Of course, we can't always avoid loud noises so easily.

  • Many critical jobs take place in loud environments or use noisy equipment,

  • like at factories, mines, and farms.

  • And farmers and factory workers need jobs, and everybody needs the stuff they make.

  • So it's not like just avoiding that noise is an option.

  • And losing your hearing can have a big effect on your life, not just your ears.

  • Like, one study in 1999 found that people with some hearing loss and no hearing aids

  • were 50% more likely to be depressed than those who used aids to restore some hearing.

  • The sensory loss and social isolation caused by impaired hearing may also be a risk factor

  • for dementia and other cognitive disorders.

  • The thing is, even if you keep your music down and work somewhere quiet,

  • noise exposure is probably still affecting your life in ways you don't even realize.

  • Most people who live in cities are frequently exposed to noise levels above 50 decibels,

  • and even a background level of 60 is not unusual.

  • Cars, trains, and planes are the most common sources of these sounds.

  • 50 or 60 decibels has no effect on your hearing,

  • but it does lead to a range of psychological responses, like getting annoyed.

  • Don't dismiss annoyance as a health consequence, by the way.

  • I, like... we've all been there.

  • Noise annoyance has been linked with a range of physical, mental, and behavioral responses,

  • from tight shoulders to depression.

  • Annoyance is especially common when our expectations for the noise level are out of sync

  • with what's actually happening.

  • For example, you probably wouldn't think twice about people chatting in the park,

  • but if it's happening in the library, that can drive you up the wall.

  • Some studies have shown that up to 40% of office workers are irritated by noise of 55 to 60 decibels,

  • while for industrial workers, the level needs to be higher than 85.

  • Noise at 85 decibels has a thousand times more power than 55,

  • so this is clearly more than just a physical effect.

  • Sound with a lot of information content, like people talking,

  • can have an outsized effect on your ability to focus, learn, and generally do, like, brain stuff good.

  • Children may be especially sensitive,

  • which isn't ideal considering most formal learning happens in childhood.

  • For example, in the early 1990s, the German city of Munich moved their major airport to a new location.

  • A major study published in 2002 tested students near the old and new sites

  • on their reading, memory, and attention skills.

  • The researchers found that, two years after the airport had moved,

  • students at the old, now-quiet site were doing measurably better,

  • while kids at the new airport were doing worse than before.

  • And the overall difference was less than 10 decibels.

  • That's why the World Health Organization recommends classrooms restrict background noise

  • to below 35 decibels, about the volume of a loud whisper.

  • But probably the most pervasive effect of background noise is sleep disturbance.

  • Sound levels as low as 33 decibels have been shown to have negative effects,

  • while volumes above 55 decibels can lead to substantial changes in mood and even sleep deprivation.

  • This is not an isolated problem, either.

  • A 2003 survey conducted in the Netherlands found that

  • a quarter of the population reported beinghighly disturbedby outside noise at least once in the last year.

  • About half those reports came from road traffic, a situation many of us can sympathize with.

  • Being woken up once in a while at night or annoyed every so often during the day

  • might seem like kind of a minor problem, but these feelings can lead to stress.

  • This may be because evolution shaped hearing as the body's critical early-warning system.

  • Sound works whether it's day or night and even if you're facing the wrong direction.

  • It's also processed by the brain much faster than vision is, and works at a subconscious level.

  • Over millions of years, we've come to associate a loud noise with something like

  • you're about to be eaten by a lion,” which is a stressful feeling.

  • And when your body is stressed, it produces higher amounts of hormones

  • like cortisol, adrenaline, and epinephrine, which affect your heart rate and blood pressure.

  • Too much of these stress hormones for too long is one way to get what doctors call hypertension,

  • better known as high blood pressure.

  • But the effects go far beyond that, including messing with your immune system

  • and even contributing to diabetes.

  • So, if you have a super loud car, please, don't drive it down my street at night.

  • Maybe the scariest outcomes, though, are cardiovascular disease and heart attacks.

  • Remember at the start, when I mentioned that the sounds around you might literally be killing you?

  • Well in 2014, the European Environment Agency estimated that noise-related health problems

  • like cardiovascular disease are responsible for ten thousand deaths each year in Europe.

  • And the World Health Organization calculates that, in all, European citizens lose more than

  • a million healthy years every single year due to traffic noise alone.

  • And if you do get ill, you might end up in the hospital.

  • And even there, you may not get the peace and quiet you need.

  • The heart rate monitor by your bed, the telephone at the nurse's station down the hall,

  • and a thousand other sounds can add up to an environment that's 15 to 20 decibels louder

  • than what the World Health Organization recommends.

  • And it's not just you that might be affected.

  • Doctors and nurses work there too, and it turns out it can be a pretty loud working environment,

  • so even healthcare comes with occupational noise risks.

  • And those people are not ones that you want to be experiencing noise-related cognitive difficulties.

  • So what can be done about all this?

  • The first thing is to simply be aware of the noise around you.

  • Apps that use your smartphone's microphone do a pretty good job

  • of estimating the volume of the ambient noise.

  • Even smartwatches are getting in on the game, alerting you to how loud your current surroundings are.

  • The rest of us will have to keep an ear out the more old-fashioned way.

  • When you're heading to a concert or a sporting event,

  • consider packing a pair of those tiny foam earplugs.

  • If you have to shout for your neighbor to hear you, it's probably a good idea to put them in.

  • That may or may not make it easier to have a conversation,