Your Teen's Phone After Bedtime: What a New Study Reveals About Sleep, Social Media, and the Developing Brain

For many parents, this scene feels familiar.

You say goodnight. Your teenager heads upstairs. The bedroom door closes. The lights go out...

...but the phone stays on.

Whether it's one last TikTok video, replying to a WhatsApp message, scrolling Instagram, or watching YouTube, smartphones have become part of many teenagers' bedtime routine. Parents often wonder: Is it really that harmful?

A new study published in JAMA Pediatrics provides some important answers.

Using objective smartphone data—not self-reports—the researchers found that nighttime smartphone use is incredibly common among adolescents and may be taking away valuable sleep during one of the most important periods of brain development.

What did the researchers study?

Researchers analysed smartphone use in 657 adolescents, aged approximately 15 years, who were participating in the large Adolescent Brain Cognitive Development (ABCD) Study in the United States.

Unlike many previous studies that asked teenagers to estimate how much they used their phones, this research used a secure monitoring app that automatically recorded which apps were being used during school nights.

The researchers focused on an eight-hour period between 10:00 p.m. and 6:00 a.m.—the time when most teenagers should ideally be asleep on school nights.

What did they find?

The results may surprise many parents.

On average, teenagers spent 50 minutes using their smartphones during school nights between 10:00 p.m. and 6:00 a.m.

Even more striking, more than 65% of that time was spent on social media apps, including YouTube, Instagram and TikTok.

Entertainment apps such as Netflix and Disney+, games, messaging platforms and music apps followed behind, but social media clearly dominated nighttime phone use.

Perhaps the most concerning finding was that over half of the adolescents (52%) used their phones during the middle of the night—between midnight and 4:00 a.m.—at least once during the study period.

For those teenagers, average use during these overnight hours was nearly 24 minutes.

Why does this matter?

At first glance, 20 or 30 minutes may not seem particularly important.

However, sleep researchers have repeatedly shown that even relatively small reductions in sleep—sometimes as little as 10 to 15 minutes per night—can affect mood, attention, learning, memory, emotional regulation and overall wellbeing.

For teenagers, this is especially important.

The adolescent brain continues developing well into the mid-twenties. During sleep, the brain consolidates learning, processes emotions, strengthens memory and supports healthy physical development.

When smartphones delay bedtime or interrupt sleep during the night, teenagers may be missing out on some of these essential restorative processes.

It's not just about screen time

One important message from this study is that timing matters.

Many parents focus on how many hours their teenager spends on a screen during the day.

But using a phone at 11:30 p.m. or 2:00 a.m. may have a much greater impact than using that same phone for half an hour after school.

Nighttime smartphone use can affect sleep in several ways. It delays bedtime because "just one more video" often turns into much longer. Notifications interrupt sleep even if the phone isn't actively being used. Exciting or emotionally engaging content makes it harder for the brain to wind down. Bright light from screens may also interfere with the body's natural production of melatonin, the hormone that helps us feel sleepy.

What does this mean for families?

This is particularly relevant for families living in the Netherlands.

Dutch teenagers are often encouraged to become increasingly independent during secondary school. Many cycle independently, manage their own homework schedules and spend more time communicating with friends online.

For international families, there can be an additional challenge. Many teenagers use their phones to stay connected with friends and relatives in different countries and time zones. While these connections are incredibly valuable, they can also make it harder to disconnect at bedtime.

The goal is therefore not to eliminate smartphones, but to help young people develop healthy habits around their use.

My professional rule of thumb

As a child and youth psychologist with more than 25 years of clinical experience, my rule of thumb is very simple:

Smartphones do not stay in bedrooms overnight. Period.

And yes—I have heard every argument under the sun.

"I use it as my alarm."

"I listen to music or podcasts to fall asleep."

"My friends might need me."

"I'm only checking one thing."

"I need it next to me just in case."

These are all understandable reasons, but they don't change the underlying issue. When a smartphone is within arm's reach, so are notifications, messages, social media, games and the temptation to keep scrolling "just a little longer."

The reality is that today's smartphones are incredibly well designed to capture—and keep—our attention. Even as adults, many of us find it difficult to resist checking "one more notification." Expecting a tired teenager, whose brain is still developing and whose self-regulation skills are still maturing, to consistently make the healthier choice late at night is often unrealistic.

Fortunately, every one of these concerns has a practical solution. An inexpensive alarm clock can replace a phone alarm. Music or podcasts can be played through a smart speaker or another device that doesn't provide instant access to social media. If parents are concerned about emergencies, families can agree on alternative ways of being contacted overnight.

Over the years, I have found that changing the environment is usually far more effective than relying on willpower alone. When phones charge overnight in the kitchen, hallway or another shared family space, many bedtime battles simply disappear. Teenagers generally fall asleep more easily, sleep more soundly and wake up feeling noticeably more rested.

This isn't about punishment or mistrust. It's about recognising that the adolescent brain deserves the best possible opportunity to rest, recover and develop.

Final thoughts

This study does not suggest that every teenager who checks their phone before bed will experience serious problems.

However, it does remind us that nighttime smartphone use is extremely common, that social media accounts for much of this use, and that many adolescents are awake and using their phones during hours when their brains should ideally be resting.

For parents, the message is encouraging rather than alarming.

Small changes to bedtime routines, combined with open conversations about sleep and technology, can have a meaningful impact on young people's health, learning and emotional wellbeing.

Sometimes, the healthiest habit isn't spending less time on a phone—it is simply knowing when—and where—to put it down.

Reference

Nagata, J. M., Kim, K. E., Leong, A. W., Christakis, D. A., Baker, F. C., & Hale, L. (2025). Smartphone Use on School Nights in the Adolescent Brain Cognitive Development Study. JAMA Pediatrics.