Double Screening on PC and Smartphone Is Wrecking Your Brain: The Hidden Cause of Unnoticed Fatigue

Working on a PC while using a smartphone. That “normal” habit might be gradually damaging your brain.

“We’ve always been told that looking at smartphones too much isn’t good,” and we understand that ourselves. The term digital detox has also become widespread, and more people are consciously trying to distance themselves.

Even so, before you realize it, you find yourself reaching for your phone. You casually open social media during work, return to your PC, and then check your phone again when a notification arrives—repeating the cycle.

What kind of effect does this double screen habit have on the brain? We asked Akihiro Morishita, a board member of the Digital Detox Association.

The real cause of fatigue is damage to the brain

Most people vaguely know that excessive smartphone use is bad for the body. Eye strain, neck pain, difficulty falling asleep—many have already experienced these issues.

At the same time, long hours of PC work can lead to stiff shoulders and eye fatigue. This too is widely recognized as a common issue with desk work.

However, what concerns Morishita the most is not the eyes or the neck—it’s damage to the brain.

“For example, if you try lifting a dumbbell with your right hand while also lifting one with your left, you’ll quickly get tired, right? But it’s harder to imagine that kind of strain when it comes to the brain. In other words, using a PC and smartphone at the same time—the double screen we do so casually—puts a heavy load on the brain.”

What makes it even more troublesome is that this fatigue is hard to notice.

“Unlike physical fatigue, brain fatigue hits later like a body blow. At first, it’s just a bit of irritability or slower work progress, but as it accumulates, it can lead to a burnout-like state. In some cases, it may even connect to mental health issues.”

It wears you down gradually without you realizing it—that is the danger of double screens.

Some people who frequently use double screens may think, “I’m good at multitasking, so I’m fine.” However, that perception needs caution.

“A study from the University of Utah found that only about 2% of people are truly capable of multitasking. Moreover, those who believe they are good at it tend to have lower efficiency and productivity in reality.”

In fact, what we think of as multitasking is, in neuroscience terms, actually called task switching.

“Think of it like driving a car—you press the brake, then the accelerator. When task B comes in while you’re doing task A, you stop A, switch to B, and then go back to A. This repeated stopping and starting is what double screen behavior really is.”

The feeling of being good at multitasking and actual performance are two different things. The more confident people are in it, the more likely they are unknowingly overworking their brains.

Even one screen can be dangerous multitasking

At this point, some might think, “Then I should just not use two screens.” But according to Morishita, it’s not that simple.

“There’s research showing that IT workers spend an average of 11 minutes on a single task. Even with just one screen, if you’re typing while checking Slack, looking at Gmail, and switching tabs, that’s no different from double screen usage.”

The core issue isn’t the number of screens—it’s the act of doing things simultaneously.

And this doesn’t apply only to work.

After getting home, you watch TV while using your phone. On the train, while walking, even in the bathroom—you’re always looking at a screen. Like a juggler spinning multiple plates, your brain never gets a moment to switch off before the day ends.

“People often ask, ‘How many hours a day should I limit my smartphone use to?’ But I tell them it’s better to stop doing things simultaneously rather than focusing on time limits. Since some switching is unavoidable during work, it’s best to start reducing it during your leisure time.”

Behind this constant multitasking is also Japanese business culture. In environments where immediate responses are expected, you feel compelled to check emails and Slack notifications as soon as they arrive. Whether working or resting, your brain is constantly required to react.

In fact, research from the University of California found that people who frequently check email tend to have higher heart rates and remain in a constant state of tension.

On the other hand, in an experiment where participants refrained from checking email for five days, screen switching decreased, focus time increased, and stress levels dropped.

“Those who checked email frequently showed higher stress responses and switched screens an average of 37 times per hour. Meanwhile, those who stayed away from email for five days said, ‘Most emails didn’t actually need such urgent replies.’”

The solution: stop bringing your phone to the restroom

So, should all interruptions during work be avoided? Morishita says, “That’s not the case.”

“There are good interruptions and bad interruptions. For example, simple exchanges related to your current task can actually serve as a refreshing break. The problem is when something unrelated that requires high concentration interrupts what you’re doing. When you’re focused on a task and get distracted by an unrelated email and feel the need to reply—that’s exactly it.”

What matters is not eliminating interruptions entirely, but creating small, frequent moments for the brain to rest. To do that, it’s important to understand the concept of attention resources.

“There’s a limit to the amount of concentration a person can use in a day. Like a smartphone battery, it decreases the more you use it. We call this attention resources, and in modern society, social media and advertising are constantly competing to capture our attention. We are continuously having our energy drained from all directions.”

As attention resources decrease, judgment becomes less clear and small things start to feel irritating. If this continues, it begins to affect work performance.

According to Morishita, “It’s not that you’re incapable of doing your job—you simply don’t have enough capacity.”

“Even with digital detox, you don’t need to suddenly stop using your smartphone for an entire day. Start by creating just five minutes where you consciously don’t touch it. Even that makes a difference.

Modern stress is micro-stress that accumulates without us noticing. To counter that, you insert short breaks called micro-breaks and gradually release it. That’s enough.”

So, where should you start?

Morishita recommends one simple step: don’t take your smartphone to the restroom.

“Just leaving your phone on your desk when you go to the restroom creates a few minutes of rest each day. If you keep that up for a week or a month, it makes a significant difference.”

Where you place your phone also matters. Many people think it’s enough to just turn the screen face down, but that’s not sufficient.

“Even if you’re not using it, if it’s on your desk, your attention still goes toward it. Even in your pocket, you might feel like it vibrated. It’s better to leave it in another room or turn it off and put it in your bag. Otherwise, it’s hard to see real effects.”

Work efficiency depends on your ability to rest

After reading this, some people might feel, “I know it’s not good, but I can’t stop.” That doesn’t mean you lack willpower.

“Realizing it in the first place is already impressive. For most people, it’s become so normal that they don’t even see it as a problem.”

According to Morishita’s estimate, modern people spend about three months a year in front of screens. That means a large portion of waking hours is spent looking at screens. In that environment, simply noticing this might not be good is already the first step.

“You don’t need to blame yourself for not being productive or for struggling to focus. It’s just that your capacity is limited. If you rest and recharge, you’ll be able to work better and expand what you can do. It’s not about ability—it’s about capacity.”

That’s why Morishita encourages having the courage to rest. And how you rest can differ from person to person.

Morishita himself resets his fatigue by going to a ski resort about an hour’s drive away. He moves his body on the snowy slopes early in the morning, works at a nearby restaurant, and then skis again. As a result, he sleeps soundly at night and works more efficiently the next day.

“Whether it’s walking, going to a sauna, or drawing, anything is fine. Finding a way to rest that suits you is like a kind of quest. There are things you only discover by trying, and that process itself is enjoyable.”

Regularly creating small moments to step away from screens can already make a difference in brain fatigue. From there, it’s about finding your own way to recharge. That’s a practical way to live with double screen fatigue.

▼Akihiro Morishita — Board member of the Japan Digital Detox Association. While working as a web media editor researching and sharing trends in digital well-being both in Japan and abroad, he is also active in lectures and events for companies and educational institutions. His book includes “Strategic Idleness — A New Way of Rest That Changes Your Life” (Asuka Shinsha).