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For most of us, our bodies are interacting with phones nearly all the time, whether we're looking at screens, listening to music, or carrying them in our pockets. If you are wondering about the health implications of a world filled with devices, here's a selection of episodes about the science of phones!

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Can Screens Damage Your Eyes?

Does Using Your Phone Hurt Your Sleep?

Do Cell Phones Cause Cancer?

Why You Think Your Phone Just Buzzed

Is There a Safe Way to Use Your Phone and Drive?

 (00:00) to (02:00)

*Intro music*

Stefan: Oh! Sorry I didn't see you there. I was just adding a few more hashtags to my latest IG. #hostlife #sciencenerd #killingit
You know when I was growing up the only carrying around miniature computers that doubled as communication devices were the cast of Star Trek. Oh how things change in just a few decades. 
Now a lot of us have cellphones and we've got questions about them too! Especially, about whether they're bad for us. So today we're going to explore what it feels like to live in a phone-filled world. 
First up is perhaps the most obvious question, what does constantly looking at this little light-up screen do to my eyes? You might have heard that phone screens are super damaging or that they're totally harmless. Well, the truth is somewhere in between, let me explain.

-----Can screens damage your eyes?-----

Stefan: If you're watching this video, you probably spend a lot of time around digital screens, like right now for example. And unless you're watching this far in the future after we've had some sort of apocalypse, there are screens all around us. So of course, a lot of people are worried that exposure to all of this unnatural light is harmful but can digital screens really hurt you?
Well, at the very least they can cause temporary annoyances like headaches but the research is still out on permanent damage. If you stare at a screen for too long, you may feel yourself feeling what's known as digital eye strain or computer vision syndrome. The most common symptoms are blurred vision, headache and pain in the neck and shoulders.
Unfortunately, even tough we know it's connected to spending a lot of time on the screen, there are a bunch of potential causes, from screen viewing making you blink less often and squint more, to it affecting your pupil response time, to it exposing you to more blue light. Or people could be suffering from digital eye strain because they don't have the right lens prescription or one that doesn't take into account astigmatism. Basically, there's no one cause!
Luckily, the symptoms of digital eye strain go away when you give your eyes a proper rest and studies haven't shown any long-term effects even if you suffer from it regularly.

 (02:00) to (04:00)

And if you want to avoid that pain in the first place, doctors recommend you take a 20 second break from your screen every 20 minutes, staring off at an object 20 feet away.

Still, there might be another way screens could harm you, and that's through exposure to blue light that can kill cells in your eyes. The color of blue light comes from its short wavelength, which also means it has high energy -- enough that blue light can damage and eventually kill the cells in your eye's retina. The light reacts with certain molecules, knocking off bits of them and creating reactive oxygen species, or ROSs, which will bond with almost anything.

They can cause so much damage that cells eventually destroy themselves in a process called apoptosis. We know this happens because researchers have done a lot of experiments. Not directly on human eyes, of course, but on animal models like rats or human retinal cells grown in petri dishes.

The thing is, most of those studies focus high-intensity light from LED lamps, and sometimes expose the subjects to that light fro day-long lengths of time. So even though we know that high-intensity blue light definitely causes retinal cell death, it doesn't tell us much about the real-life dangers of screens.

There was one 2017 study that looked at the effects of low-intensity blue light at three different wavelengths emitted from common types of screens. Specifically, they found that blue light at 449 nanometers caused the largest increase in those harmful ROSs. But light with a slightly longer wavelength of 470 nanometers didn't do much damage. That 21-nanometer change in wavelength might not seem like a lot, but the difference means that the two colors of light have different amounts of energy. The 470 nanometer light, which was a sort of turquoise, just didn't have enough energy to effectively break apart molecules. This suggests we'd do well to decrease the amount of shorter wavelength blue light from our screens if we want to save our eyeballs.

Don't shut your eyes just yet, because it ignores one major comparison: daylight. Look anywhere on a clear day, and you'll see a lot of blue, and that blue light is way more intense than what you get from staring at a computer screen. A paper published in 2016 looked at the amount of light, both in general and in the blue part of the spectrum, in a range of electronic screens and compared it against the amount of blue light you'd be exposed to from simple daylight. Its conclusion: the blue light from devices like laptops and smartphones "does not represent a biohazard, even for long-term viewing."

 (04:00) to (06:00)

So you go ahead and watch as many more SciShow videos as you want; we're officially non-hazardous.

So, the blue light from your phone might not lead to long-term eye-damage, but it can mess you up in kind of a big way -  by messing with your sleep.

Here's Hank to break it down. "Picture it - your right in the middle of binging the latest season of The Great British Bakeoff when you suddenly look at the clock, and realize it's one in the morning. You should've been in bed two hours ago, but you're not even tired. You might have even hear that artificial sources of blue light, like your laptop screen, can mess with your internal clock.

But did using a screen at night really keep you up longer, or was that just Paul Hollywood's beautiful blue eyes? And if you did bring your phone or laptop to bed with you, so that you can just watch one more episode as you drift off, will that actually prevent you from getting a good night's sleep?

Turns out, the answer to both of those questions is probably yes, and getting around the problem might not be as easy as it seems.

Your body's internal clock, or circadian rhythm, is regulated by a type of neuron in your eyes called ganglion cells. In dim light, these cells signal the release of a hormone called melatonin, which tells your body to prepare for sleep. It makes your metabolism slow down, you body temperature drop, things like that.

But these ganglion cells are more sensitive to certain colors of light than others - specifically, they are most sensitive to a wavelength of 482 nanometers, which is a sort of turquise-y blue that is a big component of daylight. 

The thing is, screens emit some blue light, too; which tricks the ganglion cells into thinking there's still some daylight out there, so it might not be time to sleep just yet.

Studies have suggested that when people are exposed to blue light before they go to sleep, they get less total sleep and wake up more frequently over the course of the night. This isn't something necessarily you could fix with a cup of coffee in the morning, either; Studies have found that long-term disruption of your body's circadian rhythm is associated with a wide range of health problems, from depression to cancer.

 (06:00) to (08:00)

Its important to note that, so far, most of the studies on blue light have been observational, meaning that they looked at what happened, but didn't control the amount of light to see if it actually caused the sleep problems. Many have also been small, or used animal subjects instead of humans.

So we don't have conclusive evidence that your daily late night scrolling actually causes sleep or health problems, but we've seen that they tend to go together. 

Let's be real here, though, most of us aren't going to stop using our phones or computers after dark, that's some of the best time for phones and computers. So there are other options, like software that makes your screen emit less blue light when it's dark out, or special glasses with tinted lenses that filter out blue light.

Unfortunatley, researchers haven't been able to consistently demonstrate that those programs or glasses actually do anything. It doesn't necessarily mean that blocking blue light is ineffective, its just that so far the studies on these approaches have had too many flaws to draw any conclusions. Maybe you're sensing a theme - we need better studies into the problems with blue light and how to address them. But for now, we know enough to say that it's probably worth stopping the TV binge just a little early, no matter how desperately you wanna find out if Stacy gets eliminated. Your body will thank you.
And no spoilers in the comments about who's the greatest British Baker!

Right, so no phones before bed, I guess I can try to do that. Speaking of dangers, though, what about daytime phone use? There's an oft repeated myth that cell phones cause brain cancer. But, here's Michael to bust that one once and for all.

A lot of people worry that their cell phone will give them cancer, which isn't all that surprising. I mean, you're holding a device that emits radiation right next to your brain - terrible idea, right? Well, no. Some kinds of radiation can damage DNA, which can then lead to cancer. But your cell phone doesn't give off that kind of radiation. 

And even if they're was a way that cell phone radiation could hurt you, studies have shown that it doesn't. 

 (08:00) to (10:00)

Cell phones communicate with cell towers using a form of radiation known as radio frequency, or RF, radiation. The word radiation is just in there because it's a type of energy on the electromagnetic spectrum. The spectrum goes from low energy at one end, to high energy at the other. Radio and microwaves are near the low end. Gamma rays and X-rays are near the high end. It can help to think of electromagnetic radiation as a wave, with a certain frequency based on its energy. The higher the energy, the higher the frequency. When an electromagnetic wave hits an atom, it transfers some energy to that atom. When the wave has a high enough frequency, meaning it has a lot of energy, it can transfer enough energy to the atom to knock out an election. Electromagnetic energy that can knock out electrons is called ionizing radiation, and it can break chemical bonds in your cells and damage your DNA. (In other words, it's the cancer-causing kind.) When electromagnetic energy doesn't have a high enough frequency to break chemical bonds, it's called non-ionizing radiation. If non-ionizing radiation hits an atom, it isn't going to be able to knock out an electron, so it can't damage cells, and it can't cause cancer. It doesn't matter how strong the beam of radiation is, its ability to knock out electrons only depends on its frequency, which isn't effected by the intensity of the radiation.

Its like your microwave - no matter how powerful it is, it's never going to start emitting infrared radiation, which would be the next level up of frequency. The cutoff between ionizing and non-ionizing radiation is somewhere on the ultraviolet range. That's above visible light and frequency, and way above the radio waves that cell phones use. Which is why, based on what we know about physics and biology, there's nothing cell phones do that can give you cancer.

However, doctors and scientists do take the potential health risks of mobile phones seriously, and a lot of studies have been done to see if there's a link between cell phones and cancer. Sometimes, these studies do find what sounds like a relationship between cell phones and cancer; at least, at first.

For example, one study of a million women in the UK found what seemed to be a weak link to a tumor called an acoustic neuroma - a benign tumor in the nerve that leads from the ear to the brain. More frequent cell phone use was correlated with a higher risk of getting this tumor. But the scientists followed the subject for 7 years. If there actually was a connection between this tumor and cell phone use, you'd expect more people to develop the tumor as they are exposed to more radiation over time.

 (10:00) to (12:00)

But the numbers didn't go up.  Based on that and the fact that other large studies haven't found the same connection; the authors of this study concluded that it was just a statistical fluke.  

Another large study from the World Health Organization found an increase in glioma among the ten percent most frequent cell phone users.  It's a type of nerve cell tumor that's responsible for most cases of malignant brain cancer.  However, there were problems with that study.

They collected data by having people report their own cell phone use.  And people tend to remember incorrectly.  Plus, people who used their cell phones less frequently had a lower risk of glioma than people who didn't use them at all.   If cell phone radiation was causing the tumors, that wouldn't make any sense.  And the vast majority of other studies have found no evidence that cell phones can cause tumors.  There's also the fact that if cell phones were causing some kinds of cancer we'd be seeing the rates of those kinds of cancers go up.  

I mean something like five billion people use cell phones, and they've been commercially available since the mid 1980's.  That's long enough for cancer to show up, even if it take's a few decades to devolop.  Which is exactly what happened after cigarettes started being mass produced.  Lung cancer used to be pretty rare.  But when smoking cigarettes started to become more popular, lung cancer rates went way up.  

There just isn't any sign of this when it comes to cell phones.  Both the number of people who get brain cancer, and the number of people who die from it, is holding steady even as cell phone use skyrockets.  
So go ahead, and make as many phone calls as you want!

Welp!  Glad to have that cleared up.
Op!  Excuse me.  Oh, weird.  I thought I was getting a call.
Have you ever had that happen?  Well, it's not weird if you have.  Because phantom vibration is a thing.  
Here's Olivia with more.

How many times has this happened to you?  Your phone buzzes, you grab it and unlock the screen, but there's no notification in sight.  You've experienced a phantom phone vibration, or what some experts call Phantom Vibration Syndrome.  The good news is that it is super common, and not harmful on it's own.  But, how often you experience these phantom buzzes, may hold clues about your mental health in general.

Results differ from study to study, but researchers are pretty sure phantom vibrations affect a lot of people.  

 (12:00) to (14:00)

Phantom ringing is also a thing, but not all studies look at both at the same time. So we're going to focus on the buzzing.

In one of the earliest studies of the subject in 2010, they found that around 68%  of participants experienced some kind of phantom buzz. This was before most people carried smartphones in their pockets, so the researchers studied medical staff, who always carried phones or pagers on vibrate mode.

In the years since then, researchers have found some factors that make you more or less likely to feel the vibrations in the first place, like a younger age, keeping your phone on vibrate, and keeping it in a breast pocket. But these mystery vibrations themselves don't seem to be doing any harm. They're more of a quirk of our normal senses.

Phantom phone vibes are likely a false alarm in something called our signal detection system, which is exactly what it sounds like. Our brain receives some kind of vague stimulus, like a light touch or dull noise, and make a decision about what it means. In the case of phantom phone vibrations, our brain has interpreted some other stimulus as a notification. That stimulus could be a familiar noise or a commonplace muscle twitch that kinda sorta maybe feels or sounds like a vibration. Plus, we expect to get notifications, and that makes our brains more likely to interpret other stimuli, or even a lack thereof, as a phone vibration. Getting false alarms from our signal detection system isn't necessarily a bad thing, but researchers have wondered if conditions like anxiety or depression might predispose us to experience false vibes more often.

One 2013 study followed 74 medical interns over the course of a year-long internship, and measured how often they felt phantom buzzes as well as any symptoms of anxiety and depression. The researchers expected the interns would feel more phantom vibrations as their stress and anxiety increased. But in the end, phantom vibes happened totally independently of the participants' anxiety. On the other hand, a different study in 2014 looked specifically at tech employees and found that phantom vibes were associated with job stress and burnout.

 (14:00) to (16:00)

So there's no clear answer yet, but if you notice yourself checking on a blank screen more often, ask yourself if you've been feeling stressed lately.

So the radiation from cell phones might not be harming our brains, but the objects themselves can kind of mess with our heads. And that's actually why it's a really bad idea to be on them while driving. Here's me again to explain.

Everyone's heard that distracted driving is dangerous, and there's a mountain of studies backing that up. Almost 400,000 Americans are killed or injured annually in distracted driving-related crashes. But people all over the world still do it anyway. In the US, drivers use phones in 88% of car trips. At least a quarter of teenagers have texted while driving, a quarter of adults say texting or emailing doesn't make their driving worse, and lots more think other distractions, like talking on the phone, aren't harmful, which just doesn't seem to add up. We're over-confident, mostly because our brains don't show us how much distractions really affect our driving, which gets us into life-or-death situations.

Ultimately the problem with distracted driving is multitasking - paying attention to multiple thoughts or tasks at once. Decades of research have shown that it doesn't matter whether you think you're great or terrible at multitasking, because humans are straight up awful at it. You make more mistakes when you're switching focus between multiple tasks, because switching takes time - anywhere from a fraction of a second to half a minute when you're driving while doing something else - and that transition time leads to missed details and mistakes. Plus, you have a sort of blindness to one task while you're focused on another, so you might think you're batting a thousand, because you don't know how much you're missing.

And that's one reason it can be tough to convince people that their distracted driving is dangerous. Research in driving simulators shows that drivers talking on their cell phones miss as much as half of what happens around them. Stop signs, exit ramps, other cars, pedestrians, you name it; and when you ask them afterwards, they just say those things weren't there.

Now, some of you are probably thinking that maybe this is true for other people, but you are a really good multitasker. Now here's the thing: more confident multitaskers do worse on multitasking tests, not better.

 (16:00) to (18:00)

And the same goes for multitasking tests that involve driving. The more comfortable a driver is with multitasking, the worse they tend to be at it. Confident or not, distracted drivers are significantly more likely to be injured, or killed, or hurt someone else. So it's a serious issue, and one that every single one of us can prevent.

But not all distractions are created equal. Adult drivers generally don't get in more accidents if they're eating or drinking, as long as it's non-alcoholic. But passengers are an interesting middle ground, because younger drivers get in more accidents when they have passengers in the car, especially people their own age. But that increased risk goes down as a driver gets older, which is actually true for most distractions.

Surveys show that younger drivers aren't as good at identifying and responding to hazards, like merging roads or swerving cars, so they choose worse times to be distracted. They're also about five to ten percent more likely to think certain distracting behaviors, like talking on the phone, don't affect their driving. But talking on the phone really does, no matter a driver's age.

Like, in driving simulations, adults are just as impaired as drunk drivers are and crash more when they're talking on the phone. And by tracking drivers' eye movements in real life and in simulations, researchers have found that drivers on the phone, or doing comparable tasks, only look at a fraction of the road.

There's also no measurable difference between holding the phone and using a hands-free device or voice recognition software like Siri, even if laws and our unaware brains say otherwise. The danger of a phone call isn't that your hand is off the wheel; it's that your attention is off the road. That's why the device doesn't matter. But talking to a passenger in the car is a little different, because they can actually see what's going on around you and, like, pause the conversation while you find your exit or merge into that lane.

Finally, researchers gathered data from cars with cameras and sensors to study about a thousand serious crashes, meaning there was property damage or injuries, and they found that texting, dialing, and reaching for the phone are about the most dangerous things that many people do while driving. Things like eating or listening to music, especially for experienced drivers, aren't tasks that demand focus from your brain. And even if your bite is a little off, or you miss a lyric here or there, who cares?

 (18:00) to (18:54)

More dangerous distractions require more of your focused attention. Because getting the details of your text conversation right often means getting the details of the road wrong. When hundreds of studies say phones aren't safe, we should listen, even if it means having some good old-fashioned silence after your podcast ends.

And there you have it. Having phones around us has changed a lot, and there are some health implications. But if we use them responsibly, like putting them away before bed, and turning them off while driving, they're really not so bad. If you wanna dig even deeper into how phones affect us, you might like the episode on our psych channel, which looks at phone addiction.

And as always, be sure to subscribe and ring that notification bell to keep up with the latest episodes of SciShow, and thank you for watching.