Previous: There Are Mountains Deep Within the Earth
Next: Why Only Some Vaccines Need Booster Shots



View count:3,024
Last sync:2021-03-24 23:30
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!

Hosted by: Stefan Chin

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Silas Emrys, Charles Copley, Drew Hart, Jeffrey Mckishen, James Knight, Christoph Schwanke, Jacob, Matt Curls, Christopher R Boucher, Eric Jensen, Lehel Kovacs, Adam Brainard, Greg, GrowingViolet, Ash, Laura Sanborn, Sam Lutfi, Piya Shedden, KatieMarie Magnone, Scott Satovsky Jr, charles george, Alex Hackman, Chris Peters, Kevin Bealer

Looking for SciShow elsewhere on the internet?
Links to Original Episodes and Sources:

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 #killing it
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 alot of us have cellphones and we've got questions about them too! Especially, about whether they are 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 alot 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, alot of people are worried atht 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 alot 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 whe 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 nueron 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 rhytm 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 demostrate 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 aproaches 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 its 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 whose 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 phones? There's an off repeated myth that cell phones cause brain cancer. But, here's my goal to bust that one once and for all.

A lot of people worry that they're cell phone will give them cancer, which isn't all that suprising. 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 radiofrequency, 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 mocrowaves are near the low end. Gamma Rays and X-rays are near the high end. It can help to think og 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, its the cancer causing kind.) When elecromagnetic 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)

 (12:00) to (14:00)

 (14:00) to (16:00)

 (16:00) to (18:00)

 (18:00) to (18:54)